1-First Step: Heat the oven and prep the dish Start by preheating your oven to 350 degrees Fahrenheit. Lightly spray a 9×13 inch casserole dish with cooking spray so the casserole does not stick. This step takes only a minute, but it helps the whole dish release cleanly after baking.

2-Second Step: Build the chicken and ham layers Spread the 5 1/2 cups shredded chicken evenly across the bottom of the casserole dish. Try to make the layer as even as possible so every serving gets plenty of chicken. Next, add the 2 cups cubed ham over the chicken in an even layer. If your ham is very watery, pat it dry first or let it drain a bit before adding it to the dish. This layering gives you the classic chicken cordon bleu recipe flavor in a simpler baked format. It also keeps the filling sturdy enough to support the creamy sauce.

3-Third Step: Make the cheese sauce Set a medium saucepan over medium heat and melt 4 tablespoons butter. Once the butter is melted, sprinkle in 1/4 cup all-purpose flour and cook for 1 to 2 minutes. The mixture should look dry and clumpy, which is exactly what you want because it helps remove the raw flour taste. Slowly whisk in 2 cups milk, pouring a little at a time so the sauce stays smooth. Use at least 2% milk to help prevent curdling, especially once the lemon juice goes in. After the milk is blended in, stir in 1 tablespoon Dijon mustard, 1 tablespoon lemon juice, 1/2 teaspoon garlic powder, and 1/4 teaspoon salt. Keep whisking and simmer for 3 to 5 minutes until the sauce thickens.

4-Fourth Step: Add the cheeses Remove the pan from the heat and stir in 1 1/4 cups shredded Swiss cheese and 1/4 cup grated Parmesan cheese. Stir until the cheese melts into a smooth sauce. Taste it and add a little more salt if needed. The sauce should be creamy, savory, and just a little tangy from the mustard and lemon.

5-Fifth Step: Pour and top the casserole Pour the cheese sauce evenly over the chicken and ham layers. Use a spoon or spatula to help spread it into the corners so every bite has that creamy coating. In a small bowl, combine 1 cup panko breadcrumbs with 2 tablespoons melted butter. Mix until the crumbs are coated, then sprinkle them evenly over the top of the casserole. For even more flavor, you can mix a little Parmesan into the breadcrumb topping. That small change gives the top a deeper taste and better browning.

6-Final Step: Bake until bubbly and golden Bake the casserole uncovered for 30 to 35 minutes, or until the topping is golden brown and the casserole is bubbling around the edges. Once it comes out of the oven, let it cool for 5 to 10 minutes before serving. That short rest helps the sauce settle a bit, so the portions hold together better.