kosher salt, plus
small elbow macaroni
salted butter, plus more for baking dish
coarse fresh breadcrumbs
( preferably homemade)
parmigiano-reggiano cheese, finely grated, about 1/2 cup
( or Pecorino Romano)
finely diced yellow onion
2 cups whole milk or 2 cups
gruyere cheese, coarsely grated
( 2 cups)
cheddar cheese, coarsely grated, preferably orange
( mild or aged cheddar, 2 cups)
freshly grated nutmeg
( or ground)
- Fill a 4- to 5-quart pot about 3/4 full of water and add 1 tablespoon of the salt.
- Bring to a boil and add the pasta.
- Cook, stirring once or twice, until tender but firm, about 4-6 minutes, and drain; reserve the pot.
- Melt 2 tablespoons butter in a medium skillet over medium heat.
- Add the bread crumbs and Parmigiano-Reggiano and cook, stirring constantly, until the crumbs are a deep golden brown, 8-10 minutes.
- Watch carefully because they can burn easily; the crumbs will continue to crisp as they cool.
- Remove immediately from the heat and set aside.
- Using the same pot you used to cook the pasta, melt the remaining 3 tablespoons butter over medium heat.
- Add the onion and cook, stirring occasionally, until soft and translucent, about 5 minutes.
- Slowly whisk in the flour and stir constantly until the onion is coated with the flour, 30-45 seconds.
- Continue stirring for 1-2 minutes more, or until the mixture starts to darken slightly and smell a bit nutty.
- Slowly whisk in the milk, cream, and remaining 1 tsp salt and cook until the mixture is just beginning to thicken and bubble around the edges, 5-7 minutes.
- It should be thick enough to coat the back of a wooden spoon.
- Add the Gruyere, cheddar, mustard powder, cayenne, and nutmeg and cook until the cheeses have melted and the sauce is smooth but not too runny.
- It should be similar in texture to cake batter; continue cooking if too soupy, until it thickens.
- Add the pasta and stir to combine.
- Ladle the mixture into individual bowls and sprinkle with the toasted bread crumbs; serve right away.