Grease an 8-inch souffle dish with the room temperature butter. Add the grated Parmesan and roll around the dish to cover the sides. Cover with plastic wrap and place into the freezer for 5 minutes.
Heat oven to 375ºF.
In a small saucepan, heat the butter. Allow all of the water to cook out.
In a separate bowl, combine the flour, dry mustard, garlic powder, and kosher salt. Whisk this mixture into the melted butter and cook for 2 minutes.
Whisk in the hot milk and turn the heat to high. Once the mixture reaches a boil, remove from the heat.
In a separate bowl, beat the egg yolks to a creamy consistency. Temper the eggs by slowly adding 1/3 of the milk mixture into the egg yolks, whisking constantly. Add the tempered egg yolks back into the milk mixture. Add the cheese and whisk until incorporated.
In a separate bowl, using a hand mixer, whip the egg whites and cream of tartar until glossy and firm. Add 1/4 of the egg white mixture to the base. Continue to add the whites by thirds, folding very gently.
Pour the mixture into the souffle dish, leaving 1/2 inch between the batter and the top of the dish. Place on an aluminum pie pan and bake in the oven for 35 minutes.