1 hour, 45 minutes
8 to 10
3 pounds waxy potatoes, unpeeled (about 7 potatoes)
3 1/2 cups milk
1/2 cup heavy cream
2 cloves garlic, crushed
1 bay leaf
2 teaspoons salt
1 cup caramelized onions
4 slices prosciutto, thinly sliced crosswise
3 ounces Gruyère, Comté or Emmentaler cheese, very thinly sliced or grated
1. Heat oven to
375 degrees and put a jellyroll pan in the bottom of the oven to catch any drips. Slice the potatoes crosswise as thinly as possible (a Japanese slicer makes this very easy).
2. Put the potatoes
in a 3-quart saucepan and add the milk, cream, garlic, bay leaf and salt. Cover and bring to a gentle simmer. When the liquid starts to bubble around the edges, remove the lid and cook until the potatoes are firm but tender, about 20 minutes in all.
3. Rub the inside
of a large gratin dish with a generous amount of butter. Using a slotted spoon, transfer about half of the potatoes to the dish and arrange in an even layer.
4. Stir together the
caramelized onions and the prosciutto and distribute this evenly across the potatoes (it will be just enough to form a very thin layer).
5. Pour the remaining
potatoes and cooking liquid into the gratin dish, arranging the potatoes in an even layer. There should be enough liquid to almost cover the potatoes. Scatter the cheese over top and bake until the top is bubbly and evenly browned, about 1 hour.
Each of 10 servings: