Preheat your oven to 375°F (190°C). Bring a large pot of salted water to a boil. Add the elbow macaroni and cook according to package directions until al dente. Drain well and set aside.

While the pasta cooks, heat olive oil in a large skillet or Dutch oven over medium-high heat. Add the ground beef and cook, breaking it apart with a spoon, until fully browned. Drain any excess grease.

Reduce heat to medium. Add the chopped yellow onion to the skillet and cook until softened, about 5-7 minutes. Add the minced garlic and cook for another minute until fragrant.

Stir in the undrained diced tomatoes, beef broth, Italian seasoning, salt, pepper, and sugar (if using). Bring the mixture to a simmer, then reduce heat to low and let it gently simmer for 10-15 minutes, allowing the flavors to meld. Taste and adjust seasonings as needed.

In the skillet with the beef sauce, add the cooked and drained macaroni. Stir well to combine, ensuring the pasta is evenly coated.

Lightly grease a 9x13 inch baking dish. Pour the macaroni and beef mixture into the prepared baking dish, spreading it evenly.

Sprinkle 2 cups of the shredded cheddar cheese evenly over the top of the casserole. Cover the baking dish loosely with aluminum foil.

Bake for 20 minutes with the foil on. Remove the foil, sprinkle the remaining 1 cup of cheddar cheese over the casserole, and continue to bake for another 10-15 minutes, or until the cheese is melted and bubbly and the top is lightly golden brown.

Remove from oven and let stand for 5-10 minutes before serving. Garnish with fresh chopped parsley, if desired.