Southern Style Macaroni and Cheese

hollow pasta, preferably elbow macaroni

1⁄2    tsp. kosher salt, plus more to taste

Butter, for greasing

plus 1 tsp. flour

extra-sharp cheddar, cut into 1⁄2" cubes (about 1 1⁄2 cups), plus 6 oz. grated (about 2 cups)

1⁄2    tsp. dry mustard

⁄4 tsp. freshly ground black pepper

⁄4 tsp. freshly grated nutmeg

⁄3 cup sour cream

eggs, lightly beaten

⁄8 tsp. cayenne pepper

1⁄2 cups half-and-half

1⁄2 cups heavy cream

Worcestershire

⁄3 cup grated onion