You can prepare to this point up to a day ahead.
Preheat oven to 400 degrees.
Pour pasta with cheese sauce into your baking dish of choice.
Top macaroni and cheese with the leftover ¼ of the Gruyere and Cheddar.
Place dish or dishes on to baking sheet lined with parchment paper.
Bake for 20 minutes. The top should turn golden brown. If it doesn’t, place under the broiler to get a golden brown crust.