Potatoes Au Gratin - Master recipes

Ingredients

• Butter for the baking dish -
• 2 tablespoons unsalted butter, melted -
• 1 cup panko breadcrumbs -
• 1 1/2 cups (6 ounces) grated Gruyere cheese, divided -
• 2 1/2 cups heavy cream -
• 1/2 cup milk -
• 3 sprigs thyme -
• 3 pounds Yukon gold potatoes, peeled and cut into 1/8-inch-thick slices -
• 1 medium yellow onion, cut into 1/8-inch-thick slices -
• 1 teaspoon salt -
• 1/8 teaspoon ground black pepper -