Cook the macaroni according to the package instructions until al dente. Drain and set aside.

In a large skillet, brown the ground beef with the chopped onion over medium heat until the beef is fully cooked.

In another pot, melt the butter over low heat. Add the flour and stir for a minute to form a roux.

Slowly whisk in the milk and cook until the sauce thickens.

Add the chili powder to the sauce and mix well.

Combine the cooked beef and macaroni with the cheese sauce, stirring until everything is well coated.

Stir in the grated cheddar cheese until melted and smooth.

Serve hot, garnished with extra cheese or chili flakes if desired.