Begin by bringing a large pot of salted water to a boil. Add the uncooked elbow macaroni and cook according to package instructions until al dente. Drain the macaroni in a colander and set aside.
In the same pot, melt the butter over medium heat. Once melted, whisk in the flour to create a roux. Cook for about 1-2 minutes until it’s bubbly and golden.
Slowly pour in the milk while continuously whisking to prevent lumps. Stir in the crushed red pepper, salt, and black pepper. Keep whisking until the mixture thickens and bubbles.
Remove the pot from the heat and add 1.5 cups of the grated extra sharp cheddar cheese, stirring until it’s completely melted and smooth.
Stir in the jar of pimentos along with their juice into the cheese sauce. This will add a delightful flavor and color to your mac and cheese.
Add the drained macaroni to the cheese sauce, stirring well to ensure every piece is coated in that creamy goodness.
Preheat your oven to 350°F (175°C). Transfer the macaroni and cheese mixture into a baking dish. Sprinkle the remaining 0.5 cup of cheddar cheese on top, then bake in the preheated oven for about 20-25 minutes or until bubbly and golden brown.