Onion Potato Gratin

Ingredients

• 1 1/2 pounds Yukon Gold potatoes, peeled, cut into 1/4 inch thick slices
• 1 large yellow onion, thinly sliced
• 2 tablespoons unsalted butter
• Salt
• 2 teaspoons Herbes de Provence, or dried thyme
• 1/2 teaspoon white pepper
• 1/2 teaspoon nutmeg
• 1 cup grated Gruyere cheese
• 8 tablespoons freshly grated Parmesan cheese
• 2/3 cup half-and-half

Directions

1. Heat the oven to 400 degrees F. In 2 quarts of water seasoned with 1 tablespoon salt, boil the potatoes for 4 minutes. Drain them, then keep them nearby.
2. Melt the butter in a large sauté pan over medium-high heat. Add the onions and cook, stirring now and then, until they have softened, about 5 minutes. Season them with salt and the Herbes de Provence, then take the pan off the heat and set it aside.
3. Arrange 1/2 of the potato slices across the base of an 11x7-inch baking dish. Season generously with salt and white pepper. Scatter about 1/3 of the Gruyere and Parmesan over the potatoes. Add the onions, sprinkle on the nutmeg, and follow with another 1/3 of the cheeses. Lay the remaining potato slices over the cheese. Pour the half-and-half over the dish, then season again with salt and pepper. Finish with the remaining 1/3 of the cheeses. If you are making this 1 day ahead, stop here, cover the dish, and refrigerate it until you are ready to cook.
4. Bake, uncovered, in the 400 degrees F oven until the liquid has thickened and the gratin is well browned, about 25-30 minutes.