Makes 12 servings. Kabocha, a Japanese winter squash with a hard rind, gives this gratin an uncommonly creamy texture.
3 cloves garlic, crushed
2 Tbsp. butter, softened
2 cups heavy cream
½ cup maple syrup
2 Tbsp. salt
½ cup minced chives
1 green kabocha squash, about 4–6 lb. (can substitute a 2½-lb. butternut squash; you should have 2 lb. of either squash after removing rind)
2 lb. garnet yams, peeled
2 lb. russet potatoes, peeled
6 oz. Gruyère-style cheese, grated
Preheat oven to 350°F. Rub garlic on the inside of the gratin dish; discard. Rub butter on interior. In a large bowl, mix cream, maple syrup, salt, and chives. Cut squash, yams, and potatoes into ⅛" slices and place in cream mix. Mix in cheese. Place squash-potato mix in gratin dish, making sure pieces lie flat. Pour excess liquid over top and press down to submerge. Bake for 30 minutes. Rotate pan and cook until lightly browned and a knife inserted in the center meets no resistance, about 30 minutes more. Let rest 15–30 minutes before serving.