This can be completely assembled up to eight hours ahead, and then it requires only a short time in the oven.

4 servings

INGREDIENTS

  • 1cup (packed) grated gruyère cheese (about 4 ounces)
  • 8tablespoons (packed) freshly grated parmesan cheese (about 2 ounces)
  • 2/3cup whipping cream1 1/2pounds yukon gold potatoes, peeled, cut into 1/4-inch-thick slices
  • 3/4pound onions, thinly sliced

    DIRECTIONS

    Combine Yukon Gold potatoes and sliced onions in heavy large saucepan. Add enough water to cover. Bring water to boil. Reduce heat and simmer until potatoes are almost tender, about 3 minutes. Drain potato-onion mixture well.


    Arrange half of potato-onion mixture in 11×7-inch glass baking dish. Sprinkle with salt and pepper. Sprinkle mixture with 1/3 cup Gruyère cheese, then 2 tablespoons Parmesan cheese. Arrange remaining potato-onion mixture atop cheeses. Pour cream over. Sprinkle with salt and pepper, then remaining 2/3 cup Gruyère cheese and 6 tablespoons Parmesan cheese. (Can be prepared 8 hours ahead. Cover and refrigerate.)
    Preheat oven to 400°F. Bake gratin uncovered until cream thickens, about 25 minutes. Remove from oven. Preheat broiler. Broil gratin until top is golden, about 2 minutes.