Instructions

1. Cook the macaroni

   1. Prepare your macaroni according to box directions.
   2. Alternatively, pour freshly boiled water over the macaroni and salt in a bowl, stir, then and let that sit while you prepare the rest of the recipe (roughly 20 minutes, but it's not strict).

2. Prepare the roux

   1. Melt butter in a saucepan, then slowly add the flour while consistently whisking.
   2. Pour the milk into the roux, whisking to combine.
   3. Whisk mustard, cayenne into the sauce, and salt to taste. Err on the side of over-salted because the cheese will dilute it a bit.

3. Prepare other ingredients

   1. Add sour cream, 1 cup parmesan, and shredded cheese into a baking dish.

4. Assemble

   1. Drain your pasta (if you haven't already) and add to in the baking dish.
   2. Pour sauce into baking dish, giving a quick mix to combine.
   3. Top the dish with breadcrumbs and remaining 1/2 cup parmesan.

5. Bake

   1. Bake at 350F for 30 minutes, then let cool a bit before slicing.