Liberally grease the Dutch Oven with the room temperature butter.
Sprinkle the parmesan cheese in and roll around the pan.
Preheat oven to 375.
Add 1 Tbsp. butter to skillet and saute Andouille, onion, peppers, and mushroom till soft. Set aside.
Add 3 Tbsp. butter to skillet and heat until the water cooks out.
Combine flour, dry mustard, garlic powder, and salt. Wisk into butter and cook for 2 minutes.
Gradually wisk in the hot milk and cook till till it's thick and bubbly.
Temper the egg yolks by gradually adding to the milk mixture a bit at a time stirring constantly.
Remove from heat and add the cheese. Stir until incorporated.
Whip the egg whites and cream of tartar and water until firm and glossy.
Gently fold the whites into the skillet mixture by thirds.
Pour the mixture into the Dutch Oven. Bake for 35 minutes and remove. Let cool for 10 minutes.
Add toppings, and return to oven for 10 minutes.