Preheat oven to 350 degrees F (175 degrees C). Grease a 9x13 inch baking dish.
In a medium saucepan, melt butter over medium heat. Stir in flour, salt, pepper, garlic powder, onion powder, thyme, and parsley. Cook, stirring constantly, until mixture is smooth and bubbly. Slowly stir in milk. Cook, stirring constantly, until mixture thickens and boils. Boil and stir for 1 minute.
Remove from heat and stir in cheese until melted. Pour over ham in baking dish.
Bake in preheated oven for 25 minutes, or until cheese is melted and bubbly.
Sprinkle with Parmesan cheese and bake for an additional 5 minutes.
Interesting Facts
This casserole is a great way to use up leftover ham.
You can add other ingredients such as mushrooms, onions, or bell peppers to the casserole.
This casserole tastes great served with a green salad or roasted vegetables.