Step 1

Preheat the oven to 350 degrees F. Butter a 9-by-13-inch baking dish and set aside.

Step 2

Cook the pasta in boiling salted water until very al dente, about 3 minutes less than the box instructions (it will finish in the oven). Drain and set aside.

Step 3

Add the milk and annatto to a 3-quart saucepan over medium-low heat and bring to a low simmer. Place 1 cup cheese snacks in the center of a double-layered square of cheesecloth. Gather the sides together to form a pouch and secure with kitchen twine. Put the pouch in the warm milk and steep for 5 minutes. Turn off the heat, then remove the pouch and discard.

Step 4

Add the butter to a 6-quart Dutch oven and let melt, then add the flour to make a roux. Whisk until smooth, then cook until blonde in color, 2 to 3 minutes. Whisking vigorously, slowly add the milk mixture. Bring to a simmer, whisking constantly, then cook, whisking occasionally, about 2 minutes more. Add the cheeses and season with salt and pepper. Mix in the pasta until fully coated. Transfer the mac and cheese to the buttered baking dish.

Step 5

Crush the remaining cup cheese snacks in a resealable bag using a rolling pin. Top the mac and cheese in an even layer with the crumbled hot cheese snacks and bake until bubbly and gooey, 15 to 20 minutes. Serve warm.