- 8 hard-boiled eggs, peeled and halved
- ¼ cup butter
- ¼ cup all-purpose flour
- 2 cups half-and-half
- ½ teaspoon salt
- ¼ teaspoon ground black pepper
- ¼ teaspoon garlic powder
- ¼ teaspoon dry mustard
- 1 cup shredded Gruyere cheese
- ½ cup freshly grated Parmesan cheese
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.