Step 1

Preheat oven to 350 degrees. Butter a 2-quart baking dish.

Step 2

Trim the leeks and cut into thin rings. Rinse thoroughly to remove all the grit. Melt butter in a skillet over medium heat. Add leeks, and cook until translucent, 3 to 4 minutes.

Step 3

Peel your potatoes and slice them into thin slices with either a mandolin or a knife. Toss the potatoes with salt, pepper, nutmeg, and thyme leaves.

Step 4

Arrange 1/2 of the potatoes in dish, slightly overlapping slices. Spread the leeks on top. Repeat with the second layer.

Step 5

In the same pan the looks were in add the garlic and sauté for 1 minute over medium-low heat. Add the cream and the mustard. Simmer for 3 to 4 minutes.

Step 6

Pour the cream over the leeks and potatoes and top with the cheese. Cover with aluminum foil and transfer to the oven. Bake for 35 minutes.

Step 7

Increase temperature to 425 degrees, uncover and bake until the cheese is bubbling and golden, 15 to 20 minutes longer. Let cool slightly before serving.