1-First Step: Prep the oven and dish Start by preheating the oven to 350°F. Spray a 9×13-inch casserole dish with cooking spray so the chicken casserole recipe does not stick. This small step saves time later when serving and cleaning up.

2-Second Step: Layer the chicken and ham Spread the 5 1/2 cups shredded rotisserie chicken across the bottom of the prepared dish. Then add the 2 cups cubed ham on top. This layering helps the flavors cook together while keeping the meat tender.

3-Third Step: Make the cream sauce Melt 4 tablespoons butter in a saucepan over medium heat. Whisk in 1/4 cup all-purpose flour and cook for 1 to 2 minutes until the mixture looks dry and clumpy. This step removes the raw flour taste and starts the thickening process. Next, slowly whisk in 2 cups milk. Add the milk a little at a time so the sauce stays smooth. Then stir in 1 tablespoon Dijon mustard, 1 tablespoon lemon juice, 1/2 teaspoon garlic powder, and 1/4 teaspoon salt. Simmer for 3 to 5 minutes until the sauce thickens.

4-Fourth Step: Add the cheese Remove the pan from the heat. Stir in 1 1/4 cups shredded Swiss cheese and 1/4 cup Parmesan cheese until melted and smooth. Taste the sauce and adjust the salt if needed. This cheesy layer is what gives the chicken cordon bleu casserole its comforting, family-style flavor.

5-Fifth Step: Pour and top Pour the cheese sauce evenly over the chicken and ham. Make sure the sauce reaches the edges so every bite stays moist. Then mix 1 cup Panko bread crumbs with 2 tablespoons melted butter in a bowl and sprinkle the mixture over the top. The buttery Panko topping gives the casserole a golden, crisp finish. If you want extra crunch, press the topping lightly into place, but do not pack it down too hard.

6-Final Step: Bake and serve Bake uncovered for 30 to 35 minutes, or until the topping is golden brown and the casserole is bubbling around the edges. Let it rest for 5 to 10 minutes before serving. That short rest helps the sauce settle, so the casserole scoops nicely.