1 hour, 15 minutes
Adapted from "Pure Dessert" by Alice Medrich. Medrich suggests serving the cake with whipped cream and peaches or nectarines splashed with Vin Santo, or with sliced oranges drizzled with honey and Vin Santo. If you have both a hand-held mixer and a stand mixer, you can use the former for the egg yolks and the latter for the whites, so you don't have to wash equipment in between.
2/3 cup sugar, divided
7 large eggs, separated, at room temperature
1/4 teaspoon salt
1/4 teaspoon grated orange zest
1/4 teaspoon grated lemon zest
2 tablespoons high-quality olive oil
1/2 cup Vin Santo or other sweet white wine, at room temperature
1/2 teaspoon cream of tartar
1 cup (3.5 ounces) sifted (before measuring) cake flour
1. Position a rack
in the lower third of the oven and heat the oven to 325 degrees. Grease the sides of a 9-inch springform pan, or 9-inch-by-3-inch cake pan with a removable bottom, and line the bottom with parchment paper.
2. In a medium bowl,
combine one-third cup of the sugar, the egg yolks, salt and both zests. In a standing mixer or with a hand-held mixer, beat at high speed until thick and light in color. Gradually beat in the olive oil, followed by the Vin Santo.
3. Put the egg whites
and cream of tartar in a large bowl and beat (at high speed if using a hand-held mixer, medium speed if using a standing mixer) until soft peaks form when the beaters are lifted. Gradually beat in the remaining one-third cup sugar and continue to beat until the egg whites are stiff but still moist when the beaters are lifted.
4. Pour half the egg
mixture over the egg whites, sift half the flour on top, and fold until nearly incorporated. Scrape the remaining egg mixture into the bowl and sift in the remaining flour. Fold just until the ingredients are blended.
5. Scrape the batter
into the prepared pan. Bake until the cake is puffed and golden, about 30 minutes. Reduce the temperature to 300 degrees and bake until a thin wooden skewer inserted in the center of the cake comes out clean, 10 to 15 minutes. If the cake is browning too fast, place a piece of buttered parchment or wax paper on top. Cool the cake in the pan on a rack for at least 10 minutes, then remove it from the pan and cool on the rack. The cake stays moist for at least 2 to 3 days if refrigerated, tightly wrapped.