Preheat oven to 350 degrees F.
Gently remove the shell from the hard-boiled eggs and cut in 1/2. Place cut side down in a baking dish greased with margarine.
In a saucepan, melt the margarine, add the flour, and cook, stirring for 2 to 3 minutes. Add the half-and-half gradually, and stir until mixture thickens and season with House Seasoning. Add the dry mustard and the Gruyere and stir until melted. Pour the sauce over the eggs and sprinkle top with Parmesan. Bake for approximately 20 to 30 minutes until bubbling and top is golden brown.
Mix ingredients together and store in an airtight container for up to 6 months.