- Coarse salt
- 1 pound elbow macaroni
- 5 tablespoons unsalted butter
- 6 tablespoons all-purpose flour
- 4 cups whole milk, room temperature
- 3/4 teaspoon ground mustard
- 1/2 teaspoon Old Bay seasoning
- 8 ounces white cheddar, shredded (3 cups)
- 4 ounces Monterey Jack, shredded (1 1/2 cups)
- 1/2 ounce Parmesan, grated (1/4 cup)
In a large pot of boiling salted water, cook macaroni according to package instructions. Drain.
In pot, melt 4 tablespoons butter over medium. Whisk in flour and cook, stirring frequently, until mixture is pale golden and has a nutty aroma, about 4 minutes.
Whisking constantly, slowly add milk. Cook, whisking along bottom of pot, until boiling, about 7 minutes. Reduce heat and gently simmer, stirring occasionally, until sauce is thickened, 10 to 12 minutes. Remove from heat and add 1 tablespoon butter, mustard, Old Bay, and cheeses. Stir until cheeses are melted and sauce is smooth; season with salt. Add macaroni to sauce and stir to combine.