Bring a large pot of heavily salted water to a boil. Add the elbow macaroni and cook according to package directions for al dente. Drain well and set aside.

While the pasta is cooking, melt the butter in a large saucepan or Dutch oven over medium heat. Once melted, whisk in the flour. Cook for 1 minute, whisking constantly, until it's bubbly and smells fragrant.

Gradually pour in the whole milk and evaporated milk while whisking vigorously to prevent lumps. Continue cooking, stirring often with the whisk, for about 5-7 minutes, until the sauce has thickened enough to coat the back of a spoon.

Remove the saucepan from the heat completely. Add the grated cheddar, Gruyère, and mozzarella in three batches, stirring until each addition is completely melted and smooth before adding the next.

Stir in the mustard powder, smoked paprika, salt, and black pepper until well combined. Add the drained pasta to the cheese sauce and stir gently until all the pasta is coated. Serve immediately.