Potatoes And Onions Au Gratin - cooking recipe

Ingredients

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

Preparation

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.