Total time: 1 hour, 45 minutes, plus 4 hours for the caramelized onions.
Servings: 8 to 10

Note: From Russ Parsons. The caramelized onions can be prepared separately. They’ll keep tightly covered in the refrigerator for at least a week.
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
Butter
1 cup caramelized onions
4 slices prosciutto, thinly sliced crosswise
3 ounces Gruyere, Comte 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 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 the top and bake until the top is bubbly and evenly browned, about 1 hour.

CARAMELIZED ONIONS
5 pounds brown onions (about 6 large)
1/2 cup oil
1 tablespoon salt
1. Cut off the stem and root ends of the onions, then halve them lengthwise and peel away the dried brown skin. Cut the onions lengthwise into one-fourth-inch-thick slices. As you finish, gather the onions in a large, heavy-bottomed pot (preferably cast iron). A 7-quart pot will work just about perfectly.

2. When all the onions have been sliced, pour over the oil and the salt and stir to combine. Set over medium heat and cover. Cook until the onions begin to wilt, stirring every 10 to 15 minutes to keep from sticking. As the onions soften, they will reduce in size quite dramatically.

3. After 20 to 30 minutes, the onions will be quite soft and will begin to stick to the bottom. Reduce the heat to low and continue cooking with the pot covered, stirring every 10 to 15 minutes to keep from sticking.

4. After 45 to 50 minutes, the onions will be silky and will be swimming in moisture. Remove the lid and increase the heat back to medium. Cook, stirring frequently, until the moisture has mostly evaporated and the onions have begun to turn golden, about 25 to 30 more minutes.

5. Once again, reduce the heat to low and continue cooking, stirring every 15 to 20 minutes, until the onions really begin to brown more deeply, about 2 more hours (this will make 2 1/2 to 3 hours total).

6. At this point, you’ll need to watch the onions very carefully, stirring every couple of minutes or so. Cook until the onions have been reduced to a deep, reddish-brown marmalade, watching that they do not dry out, about 1 more hour, making 3 to 4 hours total.
Each of 10 servings: 317 calories; 11 grams protein; 34 grams carbohydrates; 3 grams fiber; 16 grams fat; 7 grams saturated fat; 42 mg. cholesterol; 986 mg. sodium.