Preheat your oven to 375°F (190°C) and grease a baking dish with butter or nonstick spray.

In a large skillet over medium heat, melt 2 tablespoons of butter. Add sliced onions and cook until translucent and fragrant, about 10-15 minutes.

Stir in salt and pepper to taste. Sprinkle half the cheese into the skillet and mix until melted and gooey.

Transfer the onion mixture into the greased baking dish. Top with remaining cheese followed by panko breadcrumbs.

Bake for about 30-35 minutes or until bubbly and golden brown on top.

Allow to rest for about 5-10 minutes before serving.