Potato and Leek Gratin
2 tablespoons unsalted butter, plus more for greasing the pan
2 large leeks, trimmed and halved lengthwise
1 1/2 pounds Yukon Gold potatoes, peeled
1 teaspoon kosher salt
1/2 teaspoon freshly ground black pepper
2 thyme sprigs
1 cup heavy cream
1 garlic clove, finely chopped
1 bay leaf
1/4 teaspoon freshly ground nutmeg
3/4 cup Gruyère cheese, grated.
Heat oven to 350 degrees and butter a 2-quart gratin dish. Wash the leeks and slice thinly crosswise.
Using a mandoline (or knife), slice the potatoes into 1/8-inch thick rounds. Toss with 3/4 teaspoon salt and 1/4 teaspoon pepper. Layer the rounds in the gratin dish.
Melt 2 tablespoons butter in a large skillet over medium heat. Add leeks, remaining salt and pepper, and thyme. Cook, stirring, until leeks are tender and golden, about 5 minutes. Discard thyme and place the leeks over the potatoes.
Add cream, garlic and bay leaf to the skillet, scraping up browned bits of leeks from the bottom of the pan. Simmer gently for 5 minutes. Stir in nutmeg.
Pour the cream over the leeks and potatoes and top with the Gruyère. Cover with aluminum foil and bake for 40 minutes, uncover and bake until the cheese is bubbling and golden, 15 to 20 minutes longer. Let cool slightly before serving.