Grease an 8-inch soufflé mold with butter.
Add the grated parmesan and shake the mold so that the cheese covers all the sides. Cover with plastic wrap and place in the freezer for 5 minutes.
Preheat the oven to 375 degrees F.
In a small saucepan, heat the butter, allowing the water content to evaporate as it heats up.
In a separate saucepan, warm up the milk. Do not let it boil.
In a bowl combine the flour, dry mustard, garlic powder, and kosher salt. Whisk this mixture into the melted butter. Cook for 2 minutes. Whisk in the hot milk, and turn the heat to high. When the mixture comes to a boil, remove from the heat.
In a separate bowl, beat the egg yolks until creamy. Gradually add the yolks to the milk and flour mixture, whisking constantly as you pour them in. Add the Cheddar and whisk until incorporated.
In the bowl of a stand mixer, or using a hand mixer, whip together the egg whites and cream of tartar until glossy and firm.
Add ¼ of the egg whites to the other mixture, and fold gently to combine. Continue to add the whites in quarters, folding to incorporate after each addition.
Pour the mixture into the soufflé mold. Fill to 1/2 inch from the top of the mold. Place on an aluminum baking tray. Bake for 35 minutes until risen and golden. Serve immediately.