Sweet Onion Potato Au Gratin Recipe

• 2 tablespoons butter
• 1 large or 2 medium sweet onions, such as Vidalia, thinly sliced
• Salt and freshly ground black pepper
• 1/2 teaspoon ground thyme
• 1 bay leaf, fresh or dried
• 2 pounds baby Yukon gold potatoes or fingerling potatoes
• 1/2-2/3 cup heavy cream
• 1/2 cup grated Parmigiano Reggiano cheese
• 1/2 pound brick Gruyère or Swiss cheese, shredded

Directions