Potatoes Savoyarde

1 tablespoon butter

2 onions, chopped

4 pounds large Yukon Gold potatoes (about 8), peeled and cut into 1/8-inch slices

1 teaspoon salt

1/8 teaspoon freshly ground pepper

2 cups chicken or beef stock

3 ounces diced ham or cooked bacon

2/3 cup grated Gruyere or Emmentaler cheese

Preheat oven to 450 degrees F.

In a skillet, melt the butter over medium-high heat. Add the onions and saute until lightly browned, about 4 minutes.

Layer the potatoes and onions in an ovenproof casserole or baking dish and season with salt and pepper. Mix in the cooked bacon.

In a saucepan, brig the stock to a boil and pour it over the potatoes. Top with grated cheese. Bake the casserole in the oven until the potatoes are tender, about 45 minutes. Adjust the oven temperature if necessary so that the stock boils gently.