Creating this casserole is a straightforward process, inviting even the busiest home cooks to experience culinary magic in their kitchens.

1. Preheat your oven to 350°F.
2. In a medium saucepan, melt the butter over medium heat. Stir in the flour and cook for about 1 minute until it forms a paste.
3. Gradually whisk in the milk, Dijon mustard, garlic powder, salt, and pepper. Cook until the sauce thickens, about 5-7 minutes.
4. In a large mixing bowl, combine the cooked chicken, chopped ham, and half of the shredded cheese. Pour the sauce over the mixture and stir to combine.
5. Transfer the mixture to a greased 9×13 inch baking dish. Sprinkle the remaining cheese evenly over the top.
6. In a small bowl, mix the breadcrumbs with melted butter. Sprinkle the breadcrumb mixture over the casserole.
7. Bake for 25-30 minutes, or until the top is golden brown and the cheese is bubbling.
8. Let it cool for a few minutes before serving.

As you prepare this dish, picture yourself in a cozy kitchen in Monterey, the scent of garlic and herbs mingling with the ocean breeze—an experience I hold dear and hope to share with you.