Hard-Boiled Egg Casserole

Preheat oven to 350 degrees F (175 degrees C). Butter a 9-inch square baking dish.

Arrange eggs cut-side down in the prepared baking dish.

Melt butter in a saucepan over medium-low heat. Whisk flour into the melted butter until dissolved 2 to 3 minutes. Gradually stir half-and-half into flour mixture until sauce is thickened and smooth about 5 minutes. Season sauce with salt pepper garlic powder and mustard. Stir Gruyere cheese into sauce until melted and smooth.

Pour sauce over eggs and sprinkle Parmesan cheese over sauce.

Bake in the preheated oven until bubbling and golden brown 20 to 25 minutes.