Prepare a 9x13-inch baking dish by greasing it with butter or spraying with cooking spray and heat your oven to 375°F.
Bring a large pot of salted water to a boil and cook the pasta according to the package until it’s just tender. Drain well, then return the pasta to the pot.
While the pasta cooks, mix together the sharp cheddar and sharp white cheddar cheeses in a bowl.
In a medium saucepan on medium heat, melt the butter. Stir in the flour and keep whisking until the mixture turns a light golden color, about 1-2 minutes.
Slowly add in the milk while whisking continuously. Keep stirring until the sauce thickens, which should take around 5 minutes, then remove it from heat.
Season the sauce by whisking in salt, black pepper, paprika, and garlic powder. Next, fold in half of the cheese mixture until it melts smoothly.
Pour this cheese sauce over the cooked pasta and stir everything together to coat the noodles evenly.
Transfer half of the cheesy pasta into the prepared baking dish, sprinkle one-third of the remaining cheese on top, then layer the rest of the pasta over it.
Finish by spreading the remaining cheese evenly across the top.
Bake the casserole uncovered for 15 to 20 minutes, until it’s bubbling and the cheese on top has melted beautifully.