Chicken and Leek Gratin

Preheat oven to 375°F (190°C). Lightly grease an 8x8 inch baking dish.

In a large skillet, melt 2 tablespoons of butter over medium heat. Add the sliced leeks and cook, stirring occasionally, until softened, about 5-7 minutes.

Sprinkle the flour over the leeks and cook for 1 minute, stirring constantly.

Gradually whisk in the milk until smooth. Bring to a gentle simmer, stirring, and cook until the sauce thickens, about 3-5 minutes. Season with 1/2 teaspoon salt and 1/4 teaspoon black pepper.

Remove the skillet from heat and stir in the cooked chicken.

Pour the chicken and leek mixture into the prepared baking dish. Sprinkle evenly with shredded Gruyère cheese, then top with panko breadcrumbs.

Bake for 25-30 minutes, or until bubbly and the topping is golden brown.

Let rest for 5 minutes before serving.