Kale and Caramelized Onion Gratin - Circulon Cookware

Ingredients

• 3 tablespoons unsalted butter
• 4 cups red onion, chopped
• 2 tablespoons sugar
• 1 teaspoon fresh thyme leaves
• 3/4 teaspoon salt
• 1/2 teaspoon of ground black pepper
• 2 bunches kale, ] ribs removed, torn into 1 1/2-inch pieces
• 8 ounces Gruyère cheese, shredded
• 1/2 cup Parmesan cheese, grated
• 2 1/2 cups heavy cream