Place a large pot over medium heat and add the ground beef. Break it apart with a wooden spoon as it cooks, stirring occasionally until completely browned and no pink remains, about 5 to 7 minutes. Drain any excess fat from the pot.

Add the diced onion directly to the pot with the cooked beef. Sauté for 2 to 3 minutes, stirring frequently, until the onion becomes translucent and fragrant.

Stir in the macaroni, beef broth, Worcestershire sauce, garlic powder, salt, and pepper. Bring the mixture to a rolling boil over medium-high heat, then immediately reduce to a gentle simmer. Cover the pot with a lid and let it cook for 8 to 10 minutes, stirring occasionally to prevent sticking. The pasta should be tender with most liquid absorbed.

Remove the pot from heat and stir in the shredded cheddar cheese until completely melted and smooth. If the mixture seems too thick, add a splash of milk or extra broth. Let rest for 1 minute before serving.