01 - Preheat the oven to 375°F and grease a 9x13-inch baking dish.
02 - In a large bowl, whisk together the whole milk, heavy cream, softened cream cheese, Dijon mustard, garlic powder, onion powder, kosher salt, and freshly ground black pepper until smooth.
03 - Stir the shredded chicken, diced ham, and 1 1/2 cups of Swiss cheese into the sauce until evenly incorporated.
04 - Spread the mixture uniformly in the prepared baking dish. Sprinkle the remaining 1/2 cup of Swiss cheese over the top.
05 - In a separate bowl, combine panko breadcrumbs, melted butter, and grated Parmesan cheese, mixing until crumbs are evenly coated.
06 - Evenly sprinkle the breadcrumb mixture over the casserole.
07 - Bake for 25 to 30 minutes until the casserole is bubbling and the topping is golden brown.
08 - Allow the casserole to rest for 10 minutes before serving. Garnish with chopped fresh parsley if desired.