Potato, Caramelized Onion & Leek Gratin

ingredients:

• 2 tablespoons unsalted butter
• 2 large onions, chopped
• 1 large leek, white and light green parts only, thinly sliced
• 2 teaspoons salt, divided
• 1 tablespoon brown sugar
• 1 cup vegetable broth, divided
• 2/3 cup white wine
• 2/3 cup heavy or light cream
• 1 teaspoon balsamic vinegar
• 3 pounds russet potatoes, peeled and sliced 1/8 inch thick
• 2 teaspoons minced fresh thyme, divided
• 1 teaspoon black pepper, divided
• 1 1/2 cups shredded Manchego cheese

instructions:

1. Preheat oven to 350ºF.
2. Melt the butter in a large nonstick or cast iron skillet over medium-high heat. Add the onions, leek, and 1 teaspoon of salt. Cook until just beginning to brown, about 5 minutes, stirring occasionally. Stir in the brown sugar and cook, stirring frequently, until the onions are golden, about 5 minutes. Stir in 1/2 cup of the broth and cook until softened and sticky, about 5 minutes more. Transfer to a medium bowl.
3. Add the remaining broth, white wine, and heavy cream to the pan along with the remaining 1 teaspoon of salt. Scrape the bottom of the pan to release any browned bits. Bring to a boil and then remove from the heat. Stir in the vinegar.
4. In a 3-quart baking dish, scatter half of the potatoes. Sprinkle with 1 teaspoon of the thyme and 1/2 teaspoon of the black pepper. Spread the caramelized onions over the potatoes. Top with the remaining potatoes, thyme, and black pepper. Pour broth mixture over the potatoes.
5. Bake until bubbling, about 30 minutes. Top with the Manchego cheese and bake until golden brown and cooked through, about 30-40 minutes. Let cool for 15 minutes before serving.

notes:

Adapted from Cook's Country. This will turn out best if the potatoes are very thinly and evenly sliced. In order to achieve this, use a mandoline or the slicing attachment on a food processor. Gruyere cheese can be substituted for the Manchego, if desired.