Step 1

Bring a large pot or Dutch oven of heavily salted water to a boil over high heat. Meanwhile, cut 12 ounces sliced bacon crosswise into 1/2-inch pieces. Place in a large frying pan and use your hands to separate any large clumps of bacon. Cook over medium heat, stirring occasionally, until browned and crisp, 10 to 14 minutes.

Step 2

Transfer the bacon with a slotted spoon to a paper towel-lined plate. Pour 1/3 cup of the bacon fat into a heatproof measuring cup and discard any remaining fat or save for another use.

Step 3

When the water is boiling, add 1 pound dry macaroni and cook according to package directions until al dente. Meanwhile, grate 8 ounces sharp cheddar cheese and 8 ounces Monterey Jack cheese on the large holes of a box grater (about 2 cups each).

Step 4

When the pasta is ready, drain. Dry off the pot and add the reserved 1/3 cup bacon fat. Heat over medium-high heat until shimmering. Add 1/3 cup all-purpose flour and 1 1/2 teaspoons ground mustard powder and cook, whisking constantly, until fragrant and darkened in color, about 1 minute.

Step 5

While whisking constantly, slowly pour in 5 cups whole or 2% milk. Bring to a full simmer, whisking often. Reduce the heat to medium and simmer, whisking frequently, until thickened slightly, about 2 minutes. Add the cheeses and 3/4 teaspoon kosher salt, and whisk until melted and smooth.

Step 6

Add the macaroni and cook, stirring often, until heated through and bubbling, 2 to 4 minutes. Remove from the heat. Add half of the bacon and stir to combine. Taste and season with more kosher salt as needed. (If you’d like a thicker sauce, let sit for 2 to 5 minutes for it to thicken up.) Top with the remaining bacon.