Cook the gluten-free elbow macaroni noodles according to the package directions. I personally like to take 2 minutes off of the cooking time so that my pasta is al dente. Drain the pasta and set aside.
Place a large skillet or saucepan on the stove top over medium heat. Add the unsalted butter and melt.
Once the butter is melted, add the gluten-free all-purpose flour, salt, ground mustard, onion powder, and black pepper. Whisk until a paste forms, about 1-2 minutes.
Pour in the whole milk. Whisk until the mixture has thickened, about 3-5 minutes.
Sprinkle in the shredded mozzarella cheese and parmesan cheese.
Mix until the cheese is completely melted.
Add the cooked pasta back into the pan.
Fold the pasta into the cheese sauce. Top with fresh basil if desired. Serve immediately.