Preheat the oven to 375°F. (no fan) Butter a 2.5-liter glass or Pyrex baking dish or casserole dish, or leave it unbuttered. I did and life went on. Casserole dishes also work.

Bring 2 quarts of water to a boil in a large saucepan and add a generous amount of salt. You can taste the water if you want - it should taste salty like the ocean.

Add the elbows to the large pot of salted water and stir to distribute and keep from sticking. Boil over medium heat until they are al dente or completely cooked. I like to cook them completely because 15 minutes isn’t a long additional bake time and I don’t want undercooked pasta in my mac and cheese. Drain pasta through a colander or strainer and set aside.

Melt butter in a 3-4 quart saucepan. Add flour, ½ teaspoon kosher salt (if using unsalted butter), and mustard powder, whisking until smooth. Bring to a boil and boil for 1 min on medium heat, while whisking constantly. Try not to let it brown. If it does, no big deal—just keep going!

Slowly add milk a little at a time, whisking constantly until all the milk has been added. It will be loose and liquidy, do not stress.

Reduce the heat to medium-low and continue to cook the roux, stirring frequently until thickened. It will be thick like cream and will coat the back of a spoon.

Remove from heat and stir in the cheese.

Add pepper and paprika, stirring well. Taste and add salt if desired. If you salted your pasta water, this shouldn’t be necessary.

Stir in the cooked pasta and pour into the baking dish. Sprinkle with reserved cheese. Bake the dish uncovered at 375°F until the center is bubbling and the top is golden brown. 15-20 minutes. Can broil the last 3 minutes to get a nice golden top.