In a large skillet or Dutch oven over medium heat, cook the chopped bacon until crispy. Use a slotted spoon to remove the bacon to a paper towel-lined plate, leaving about 1 tablespoon of grease in the skillet.

Add the diced onion to the skillet and cook for 3-4 minutes until softened. Add the ground beef and cook until fully browned, breaking it apart with a spoon. Drain off any excess grease. Stir in the minced garlic and cook for 1 minute more until fragrant.

Stir in the beef broth, ketchup, mustard, Worcestershire sauce, salt, and pepper. Bring to a simmer. Add the uncooked pasta and stir to combine, making sure the pasta is submerged. Bring to a boil, then reduce the heat to low, cover, and simmer for 12-15 minutes, stirring occasionally, until pasta is al dente.

Turn off the heat. Slowly pour in the heavy cream and stir to combine. Add the shredded cheddar and American cheese slices. Stir continuously until the cheese is completely melted and the sauce is smooth and creamy.

Stir in half of the crispy bacon. Serve immediately, garnished with the remaining bacon and fresh parsley, if desired.