1-First Step: Prep the Oven and Dish: Preheat the oven to 350 degrees Fahrenheit. Spray a 9×13 casserole dish with cooking spray so the casserole does not stick. This small step makes serving much easier later.

2-Second Step: Build the Base Layers: Spread 5 1/2 cups of shredded rotisserie chicken evenly across the bottom of the casserole dish. Then layer 2 cups of cubed ham over the chicken. Try to keep the layers even so every serving gets a little bit of both. If you are using leftover chicken, this is a great way to turn it into a fresh meal without extra work.

3-Third Step: Make the Cheese Sauce: Set a saucepan over medium heat and melt 4 tablespoons butter. Sprinkle in 1/4 cup all-purpose flour and cook for 1 to 2 minutes. The mixture should look dry and clumpy. This is normal and helps the sauce thicken properly. Slowly whisk in 2 cups milk. Keep whisking while you add 1 tablespoon Dijon mustard, 1 tablespoon lemon juice, 1/2 teaspoon garlic powder, and 1/4 teaspoon salt. Let the sauce simmer for 3 to 5 minutes, stirring constantly, until it thickens.

4-Fourth Step: Finish the Sauce: Take the pan off the heat. Stir in 1 1/4 cups shredded Swiss cheese and 1/4 cup grated Parmesan cheese until smooth and melted. Taste the sauce and add a little more salt if needed. If you want a richer and saucier baked chicken cordon bleu casserole, you can make a little extra sauce at this stage. Keep the milk at 2% fat or higher. Lower-fat milk can curdle more easily when combined with mustard and lemon juice.

5-Fifth Step: Assemble the Casserole: Pour the cheese sauce evenly over the chicken and ham in the baking dish. Try to cover the full surface so the casserole bakes evenly and stays creamy in every bite. If you want to add cooked rice or noodles at the bottom, this is the point where you can do that for a heartier meal.

6-Sixth Step: Add the Panko Topping: In a small bowl, mix 1 cup Panko bread crumbs with 2 tablespoons melted butter. Sprinkle the mixture evenly over the top of the casserole. For a more flavorful topping, you can also mix in a little grated Parmesan cheese or a pinch of paprika.

7-Seventh Step: Bake Until Bubbly: Bake uncovered for 30 to 35 minutes, or until the top is golden brown and the casserole is bubbly around the edges. The smell alone will probably bring everyone into the kitchen early, so be ready.

8-Final Step: Rest and Serve: Let the casserole cool for 5 to 10 minutes before serving. This helps the sauce set slightly, so your portions hold together better. Serve it as a full meal or spoon it over pasta or rice to stretch servings for a larger crowd.