Cook elbow pasta according to instructions on box. Set aside.
Preheat sauté pan, once hot crumble ground beef into pan. Once beef has browned a quarter of the way add onions. Cook until onions are translucent and ground beef has completely browned.
Strain excess fat from beef and onions, and set aside.
In a large saucepan melt butter, then add tapioca flour to make a roux.
Gradually add milk to saucepan and bring to a boil, stirring constantly. Once mixture has thickened, remove from heat and add grated cheese.
Mix until cheese is melted, then add beef/onion mixture and cooked pasta to cheese sauce. Mix until well incorporated. Enjoy with a simple green salad!