Potato and Onion Gratin - Draeger's Market

Ingredients

• 1 tablespoon unsalted butter
• 1 ½ pounds Yukon Gold potatoes, peeled and cut into ¼-inch thick slices
• 1 yellow onion, thinly sliced
• Kosher Salt
• freshly ground black pepper
• 1 cup grated Gruyere cheese (about 8 ounces)
• ½ cup grated Parmigiano-Reggiano cheese
• 2/3 cup heavy cream
• ½ teaspoon freshly grated nutmeg
• ½ cup panko breadcrumbs