Holiday Desserts : What Crust! Susan Purdy’s Pie Primer : Baking: To help home cooks turn out perfect pies, cookbook author has devised a foolproof pastry crust.

Susan G. Purdy knows the troubles home bakers face. She knows the disappointment of rolling out pie dough only to watch it fall in shreds when it’s lifted from the board. She understands the frustration that drives people to ready-made crust and store-bought pies.

That’s why Purdy, cooking teacher, cookbook author and expert pie baker, set out to make the perfect, foolproof flaky pastry dough. She came up with a dough that is so tender and yet so sturdy that Purdy, demonstrating the recipe in the The Times’ Test Kitchen, is now lifting the rolled-out circle and flapping it in the air.

“I have a real sweet tooth,” she says as she pats the dough in a pie pan, “which is why I write about desserts and not salads.”

She has written two books: “As Easy as Pie” (Collier Books softcover edition: $14.95), first published in hardcover in 1984 and just released in paperback, and “A Piece of Cake” (Atheneum, $24.95), which came out last year. As the titles imply, Purdy believes baking shouldn’t intimidate.

“As Easy as Pie,” for instance, gives the recipe for her foolproof pastry dough, but realizing that pie crust frightens many, she suggests an easier crumb crust for many pies. The combinations of crumbs, sugar and butter are not rolled but merely pressed onto the pie plate and chilled or baked. A three-page chart in her book tells at a glance how to make a baker’s dozen of these.

Fruit cobblers and crisps are another escape from traditional pie crusts that meet Purdy’s approval. These are easy because the topping is simply spooned or sprinkled over the fruit.

But for classic American pie, a pastry shell is a must. And if you’re ready to tackle one, here is Purdy’s five-point guide to success:

1. Have everything cold. Purdy stores butter and margarine in the freezer. She knows bakers who keep flour in the freezer and chefs who refrigerate the marble slab on which they roll out pastry. For liquid, use ice water.

2. Use lemon juice or white vinegar and an egg yolk as part of the liquid. The acid agent inhibits the gluten in the flour, and the egg yolk makes the pastry easier to handle.

3. Use a minimum amount of liquid. After adding the lemon juice and egg yolk, sprinkle on ice water a tablespoon at a time until the dough just starts to cling together.

4. Handle the dough as little as possible. If using a food processor, stop processing as soon as the ingredients form small crumbs. Letting it spin until the dough forms a ball guarantees an overworked, tough crust.

5. Place the pie in the oven at high heat--425 degrees. This will turn the water to steam, which will make the little flecks of fat and flour in the pastry rise and separate. If the oven temperature is too low, the fat will melt and be absorbed by the flour along with the liquid, resulting in a tough, pasty crust. Gauge the heat with an oven thermometer rather than trusting the oven control. “Most home ovens are irregular,” Purdy says, and the actual heat may be substantially different from that indicated by the control.

Purdy typically starts a pie in the lower third of the oven, bakes it for about 12 minutes at 425 degrees, then raises it to the oven center and lowers the temperature to 350 degrees, or, for a custard pie, 325 degrees.

She suggests using a glass pie plate rather than a pan in order to check the browning of the crust. And she avoids heavy black pie pans. “They get the crust too tough,” she says.

For Thanksgiving, Purdy suggests a rum-flavored pumpkin chiffon pie that is ideal for inexperienced cooks because it has a crumb crust and can be made a day in advance. Purdy herself sometimes omits the crust and piles the filling in wine goblets. “It’s a soft, light mousse held together with a little gelatin,” she said.

For Christmas, she’s devised an unusual Cranberry-Pecan Pie. “The color is beautiful,” she says, and the cranberries cut what she calls “the awful cloying sweetness of pecan pie.”

Her choice for New Year’s Eve is a Velvet Rum Cream Pie decorated with chocolate leaves. And for any occasion, she recommends an unusual concoction of dried apricots, raisins and sour cream that is baked in a pastry crust. “It’s not too sweet, and yet it’s quite rich,” she says. “It seems to please everyone.”

The basic pastry recipe that follows emphasizes the techniques that Purdy believes will yield the best results for a beginner. In it, frozen butter and margarine are used and the dough is mixed in a food processor. In her book, the recipe is given in greater detail, covering other methods for mixing and suggesting ways in which to vary the flavor by adding nuts, coconut, cocoa or, for savory pies, herbs and cheese.

BASIC ALL-PURPOSE FLAKY PASTRY

2 cups flour, sifted

3/4 teaspoon salt

1/2 cup unsalted butter, frozen

3 tablespoons margarine, frozen

1 large egg yolk

2 tablespoons lemon juice

3 to 4 tablespoons ice water

Measure flour and salt into food processor work bowl fitted with steel blade. Cover and pulse quickly 2 or 3 times to lighten dry ingredients. Uncover and add cut-up frozen butter and margarine. Process 5 to 10 seconds until dough has texture of rough cornmeal.

Through feed tube, add egg yolk and lemon juice. Pulse 2 to 3 times. Add ice water little at time, following each addition with 2 quick pulses, until dough starts to clump together but still looks rough and lumpy. Specks of yolk and butter may still be visible. If dough appears too dry and crumbly, sprinkle on little more water and pulse once more. Use only as much ice water as needed.

Turn off processor, uncover and pinch dough. If dough holds together, it is done. Do not process until dough forms ball on steel blade or pastry will be overworked and tough. Dough may be rolled out at once. Or turn out onto wax paper, lift opposite corners of paper and press on dough, forming it into ball. Wrap and refrigerate until needed. Makes enough pastry for 1 (2-crust) 8- or 9-inch pie, with some dough left over for trimming, or 1 (1-crust) 11- or 12-inch pie or 9 (4-inch) tart shells.

APRICOT-RAISIN-SOUR CREAM PIE

Unbaked pastry for 1 (10-inch) pie shell

1/3 cup seedless raisins

2/3 cup dried apricot halves, packed

2 cups sour cream

2 eggs

1 cup granulated sugar

1/4 cup flour

1/4 teaspoon salt

Grated zest of 1 orange

1 teaspoon vanilla

Powdered sugar

Prepare pastry, roll out and fit into 10-inch pie plate. Trim overhang to 3/4 inch. Fold over edge and flute as desired. Chill while preparing filling.

Measure raisins into small bowl and cover with boiling water. Let stand to plump about 20 minutes. Cut apricots into small pieces (approximately in quarters). Place in saucepan and cover with water. Cover pan and bring to boil, then lower heat slightly and simmer apricots 10 minutes. Drain in sieve or colander.

With electric mixer, beat together sour cream, eggs, granulated sugar, flour, salt, orange zest and vanilla. Strain raisins, discarding liquid, and add with apricots to sour cream mixture. Stir well to distribute fruit evenly. Pour into prepared pastry shell.

Place in lower third of 400-degree oven and bake 40 to 45 minutes, until light golden on top and stainless-steel knife inserted into custard 1 inch from edge comes out clean. Cool on wire rack. (Pie filling puffs slightly as it bakes, then sinks as it cools.) Serve at room temperature. Just before serving, sift powdered sugar lightly over top. Makes 1 (10-inch) pie.

RUM-PUMPKIN CHIFFON PIE

1 (9-inch) Gingersnap Crumb Crust

1 envelope unflavored gelatin

1/4 cup water

3 eggs

2/3 cup sugar

1/2 teaspoon salt

Generous 1/2 teaspoon ground cinnamon

Generous 1/2 teaspoon ground nutmeg

Generous 1/2 teaspoon ground ginger

3 to 4 tablespoons dark rum or triple sec

1 1/4 cups canned pumpkin

1/2 cup whipping cream

Rum-Flavored Whipped Cream

Almond slices or candied ginger slivers

Freshly grated nutmeg

Prepare crust and chill while preparing filling.

Sprinkle gelatin over water in small saucepan. Let stand 2 minutes to soften, then stir over low heat until thoroughly dissolved. Cool.

Separate eggs, placing yolks in top of double boiler and whites in large bowl of electric mixer. Add 1/3 cup sugar to yolks and whisk until mixture is thick and light lemon-colored. Add salt, cinnamon, nutmeg and ginger, rum and dissolved gelatin. Whisk together. Set over boiling water and stir constantly over medium heat until mixture becomes very thick and generously coats spoon.

Remove from heat, stir in pumpkin and whisk to combine thoroughly. Turn mixture into clean, cool mixing bowl and place in large bowl of ice water. Whisk about 15 minutes to cool mixture until it feels thick, mounds on spoon and looks as if it is beginning to set. Do not chill until it sets hard. Remove bowl from ice water.

Beat egg whites until fluffy, then add remaining 1/3 cup sugar little at time, beating after each addition until stiff peaks form and whites are very satiny. With chilled bowl and beaters, whip cream to medium-stiff peaks. Fold pumpkin mixture into whipped cream, then into egg whites. Spoon into prepared crust. Cover with plastic wrap and chill at least 3 hours to set.

Just before serving, spoon Rum-Flavored Whipped Cream into ring around edge of pie, or pipe into rosettes with pastry bag fitted with star tip. Decorate with almonds or ginger and sprinkles of nutmeg. Makes 1 (9-inch) pie.

Gingersnap Crumb Crust

1 1/3 cups gingersnap crumbs, made from 25 (2-inch) cookies

5 1/3 tablespoons melted butter or margarine

Place crumbs in bowl, add butter and toss to coat. Press evenly over bottom and sides of 9-inch pie plate. Chill until firm or bake at 375 degrees 6 minutes.

Rum-Flavored Whipped Cream

1 cup whipping cream

2 tablespoons rum or 1 teaspoon rum extract

3 tablespoons powdered sugar, sifted

Whip cream to soft peaks, add rum and powdered sugar and whip to firm peaks. Chill or use immediately.

CRANBERRY-PECAN PIE

Pastry for 9-inch pie shell

3/4 cup dark brown sugar, packed

3 eggs

6 tablespoons unsalted butter, melted

2/3 cup dark corn syrup

1 tablespoon unsulfured molasses

1 teaspoon lemon juice

1 teaspoon vanilla

1/4 teaspoon salt

3/4 cup pecan halves

3/4 cup coarsely chopped fresh or frozen cranberries

If desired, make pastry with half each whole-wheat and all-purpose flours, or use any favorite pastry. Roll out pastry and line 9-inch pie plate. Trim overhang to 3/4 inch. Fold over edge and flute as desired. Pierce bottom all over with fork. Chill pastry until firm.

Cut square piece wax paper, parchment or foil slightly larger than pie plate and set over pastry. If using foil, place shiny side down. Fill liner half full with pie weights, rice or beans. Bake at 425 degrees 10 minutes. Cool on wire rack. Lower oven to 400 degrees.

Combine brown sugar and eggs in bowl of electric mixer. Beat until well blended and free of lumps. Add melted butter, corn syrup, molasses, lemon juice, vanilla and salt. Beat well. Pour filling into prepared shell. Arrange pecans and cranberries over top.

Bake in center of 400-degree oven 20 to 30 minutes, until knife inserted in center comes out clean. Cool on wire rack. Serve at room temperature, topped by vanilla ice cream or slightly sweetened whipped cream.

VELVET RUM CREAM PIE

1 (10-inch) Graham-Nut Crumb Crust or 1 (10-inch) completely baked pastry shell of choice

1 envelope unflavored gelatin

1/2 cup cold water

6 egg yolks

1 cup granulated sugar

1/3 cup plus 1 tablespoon dark rum

2 cups whipping cream

1 tablespoon powdered sugar, sifted

Chocolate leaves, curls or grated chocolate

Prepare Graham-Nut Crumb Crust and chill while preparing filling. Sprinkle gelatin over cold water in small saucepan. Place over low heat and stir constantly while bringing to just below boiling point to dissolve gelatin. Remove from heat.

Beat egg yolks with granulated sugar until thick and light-colored and mixture forms flat ribbon falling back upon itself when beater is lifted. Stir in hot gelatin, which will melt sugar. Gradually add 1/3 cup rum while beating slowly.

In chilled bowl with chilled beaters, whip 1 1/2 cups cream until stiff peaks form. Fold cream into gelatin mixture. Set bowl into large bowl of ice water and whisk 10 to 15 minutes, until mixture feels thick, mounds on spoon and looks as if it is beginning to set. Immediately remove bowl from ice water and spoon filling into pie shell. Cover with plastic wrap and chill at least 4 hours to set.

Shortly before serving, whip remaining 1/2 cup cream. When soft peaks form, add powdered sugar and rum, then beat cream medium stiff. Spoon into ring around edge of pie or pipe into rosettes through pastry bag fitted with star tip. Decorate with chocolate leaves, curls or sprinkling of grated chocolate.

Graham-Nut Crumb Crust

1 cup graham cracker crumbs

3/4 cup ground almonds

5 tablespoons sugar

1/2 cup melted butter

Combine cracker crumbs, nuts and sugar in bowl. Add butter and toss to coat. Press over bottom and sides of 10-inch pie plate. Chill until firm or bake at 350 degrees 8 minutes.

Because of the Thanksgiving holiday there will be no Food Section on Thursday. However, in addition to today’s section, there will be a Food Section on Friday.