In a large pot, bring salted water to a boil. Add the elbow macaroni and cook according to package instructions until al dente. Drain and set aside.
In a large skillet, melt the butter over medium heat. Once melted, whisk in the flour until smooth, creating a roux. Continue to whisk for about 1-2 minutes to cook out the raw flour taste.
Gradually pour in the milk while whisking constantly to avoid lumps. Bring the mixture to a simmer, allowing it to thicken slightly.
Add the crushed red pepper, salt, and black pepper to the sauce. Stir well to combine.
Add 1½ cups of the grated extra sharp cheddar cheese to the sauce, stirring until melted and creamy. Remove from heat.
Add the cooked macaroni to the cheese sauce, stirring to coat all the pasta evenly.
Stir in the pimentos, including the juice, for a burst of flavor.
If you prefer a baked version, preheat your oven to 350°F (175°C). Transfer the mac and cheese to a baking dish, sprinkle the remaining ½ cup of cheddar cheese on top, and bake for 20-25 minutes until bubbly and golden.
