This is a favorite of ours for company during the autumn and winter months. It is takes a little time and it is worth it.
1 ½ cups whipping cream
2 large leeks (white and pale green parts only), halved lengthwise, cut into ¼ inch thick slices
2 Tablespoons chopped fresh thyme or 2 teaspoons dried
1 teaspoon salt
¼ teaspoon ground white pepper
¼ teaspoon ground allspice
¼ teaspoon ground nutmeg
1 pound yams, peeled, cut into ¼ inch thick slice
1 pound Granny Smith apples (or equivalent variety), peeled, halved, cored, cut into 1/8 inch thick slices
1 cup grated white cheddar cheese
Preheat oven to 350 ºF. Butter an 8-inch square baking dish. I use an oval dish that is ~ 8 x 11 inches.
Bring cream and leeks to a boil in a heavy large saucepan. Reduce heat, cover and simmer until leeks are tender, ~15 minutes. Add thyme, salt, pepper, allspice and nutmeg.
Arrange 1/3 yams in bottom of prepared dish. Ladle 1/3 of leek mixture over. Cover with half of apples. Sprinkle with 1/3 cup cheddar cheese. Arrange 1/3 of yams over. Ladle 1/3 of leek mixture over. Cover with remaining apples. Sprinkle with 1/3 cup cheese. Arrange remaining yams over. Ladle remaining leek mixture over. Sprinkle with remaining cheese.
Cover with foil and bake 30 minutes. Uncover and bake until brown, about 45 minutes. Cool slightly.