Pour hot water into the thermos for 15 minutes to get it hot.

Cook the pasta according to package directions. Drain and set aside. Warm 1 cup of milk over medium heat.

Whisk together the remaining milk and flour until there are no lumps.

When the milk begins to steam, whisk in the flour mixture. Whisk until it begins to thicken, about 3 to 4 minutes. It will be the consistency of heavy cream. Gradually whisk in the cheese.

Add salt, pepper, dry mustard, cayenne, and nutmeg.

When the cheese has completely melted, add the pasta.

Coat the pasta completely in cheese sauce.