Scalloped Potatoes with Leeks

INGREDIENTS

• 2 tablespoons unsalted butter, plus more for baking dish
• 2 leeks, trimmed, thinly sliced, and rinsed well (about 1 cup)
• 6 russet potatoes (2 1/2 pounds), peeled and thinly sliced
• 1/2 teaspoon coarse salt
• 1/8 teaspoon freshly grated nutmeg
• Freshly ground pepper, to taste
• 8 ounces Gruyere cheese, shredded (about 3 cups)
• 1 cup heavy cream
• 1 cup homemade or low-sodium store-bought chicken stock