Step 1

Preheat the oven to 350 degrees F (175 degrees C). Spray a 9x13-inch baking dish with cooking spray.

Step 2

Bring a large pot of water to a boil. Add macaroni and 2 ½ teaspoons salt and cook, stirring frequently, for 5 to 6 minutes. Drain and set aside.

Step 3

Shred Cheddar cheese by hand or in a food processor; set aside.

Step 4

Melt butter in a large saucepan over medium heat. Whisk in flour and cook, whisking constantly, until smooth, 3 to 4 minutes. Whisk in mustard powder, then 3 ½ cups milk. Whisk occasionally until mixture comes to a simmer, then let simmer for 5 minutes.

Step 5

Add cream cheese and cook, stirring often, until thick, creamy, and smooth, about 5 minutes. Add remaining 1 ½ teaspoon salt, pepper, and cayenne.

Step 6

Stir in 2 cups shredded Cheddar. Turn off the heat and let cheese melt. Stir in cooked macaroni. Add up to ¼ cup milk if you feel like the mixture is too thick.

Step 7

Layer ½ of the pasta mixture in the bottom of the prepared baking dish. Top with 1 ½ cups Cheddar. Spread remaining pasta mixture over top and sprinkle with remaining Cheddar.

Step 8

Bake in the preheated oven until golden and bubbly, 25 to 30 minutes.