I've not made this but ran across the recipe in a novel. It sounds really good:
Goldy's Prudent Potatoes au Gratin from Diane Mott Davidson
Secret ingredient make this au gratin dish a new favorite
Servings: 8 Servings
Total Time (median): 1 : 40 Active Time: 0 : 40
Ingredients
* 1/2 tablespoon unsalted butter
* 1 tablespoon olive oil
* 1 large yellow onion (trimmed peeled & very thinly sliced) about 2 cups
* 4 lbs russet potatoes
* 1/2 lb Gruyere cheese grated
* 1/2 lb Comte or Fontina cheese grated
* 1/2 c freshly grated Paremesan cheese
* 1 tablespoon finely chopped fresh sage
* 1 teaspoon sea salt (or kosher salt)
* 1/2 teaspoon freshly ground black pepper
* 2 cups heavy cream
Preparation
Butter a 9X13 inch glass baking pan.
Melt butter with oil over medium-low heat in a large saute pan. Add onion and cook over low heat, stirring frequently, until the onion is very limp & has carmelized without burning. (approx 15-25 min).
Preheat over to 375 degrees F
Peel & slice potatoes thinly. Toss together the grated cheeses. Place a layer of sliced potatoes in the prepared pan, followed by a scattering of the cooked onions. Sprinkle on a layer of cheese, then sprinkle on some of the sage. Continue to layer until all ingredients are used up & end with a layer of cheese.
Stir the salt & pepper into the heavy cream & pour slowly all over the potato mixture without disturbing the cheese topping. Bake in the middle of the oven for about 1-1.5 hrs. Top should be golden brown and potatoes very tender.
