In a large skillet, heat over medium-high heat and add the ground beef, breaking it up with a spatula. Brown the beef for about 3 minutes, then stir in the chopped onions. Sauté until the beef is fully cooked and the onions have softened, about 5-6 minutes. Drain any excess fat.

In a large pot of salted water, bring to a rolling boil. Add the macaroni and cook until al dente, around 7-9 minutes. Drain and set aside.

In the same skillet, melt about 2 tablespoons of butter over medium heat. Add minced garlic, stirring for about 30 seconds until fragrant. Whisk in flour to create a roux, cooking for 1-2 minutes until golden. Gradually incorporate the tomato sauce, bring to a boil while stirring, then reduce heat and let simmer for 3-5 minutes until thickened.

Return the cooked beef to the skillet and mix well. Add drained macaroni and combine thoroughly. Gradually sprinkle in the cheddar cheese, stirring until melted and evenly distributed.

Allow to sit for a minute to let flavors meld, then serve warm, optionally topping with additional cheese.