Potatoes And Onions Au Gratin
["8 c. thinly sliced onions", "1 1/2 sticks unsalted butter or margarine", "2 lb. baking potatoes, peeled and cut into 1/8-inch slices", "2 c. heavy cream", "1/2 c. freshly grated Parmesan cheese", "1/2 c. grated Gruyere cheese"]
["In a large skillet, cook the onions with salt and pepper to taste in 6 tablespoons butter over moderate heat, stirring occasionally, until they are golden.", "Spoon half the onions into a buttered 4-quart gratin dish; cover them with the potato slices, then sprinkle with salt and pepper.", "Cover the potatoes with the remaining onions; pour the cream over the mixture and sprinkle the mixture with the combined cheeses.", "Dot the top with the remaining 6 tablespoons butter and bake the gratin in a preheated 400\u00b0 oven for 30 minutes or until tender and golden brown."]
["onions", "butter", "baking potatoes", "heavy cream", "freshly grated Parmesan cheese", "Gruyere cheese"]