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 and rinse 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, 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 cheddar cheese and grated 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 parsley or additional spices if desired. Serve immediately.