First, cook your bacon until it's wonderfully crispy. You can do this in the oven on a sheet pan or in a skillet. Once done, drain it well on paper towels and then chop it into small pieces. Set these aside for later.
While the bacon cools, cook the elbow macaroni according to the package directions until it's al dente. Drain the pasta thoroughly and set it aside.
In a large skillet, brown the lean ground beef over medium heat until it's fully cooked through. If there's any excess fat, feel free to drain it off, though using lean beef helps keep some flavorful juices.
In a small bowl or measuring cup, whisk together the beef broth, Worcestershire sauce, and ketchup. In a separate tiny bowl, mix the cornstarch with a tablespoon or two of the broth mixture until smooth – this prevents clumps. Then, add this smooth cornstarch slurry to the rest of the broth mixture and stir everything well.
Add the cooked pasta to the skillet with the browned beef. Pour in the beef broth mixture and stir everything together to combine the beef, pasta, and chopped bacon with the sauce.
Continue cooking this mixture over medium heat, stirring occasionally, until the sauce begins to bubble and thickens up nicely. If it gets too thick, you can thin it slightly with a splash more beef broth.
Finally, sprinkle both the shredded cheddar and mozzarella cheeses evenly over the top of the hot skillet mixture.
Cover the skillet and let it cook on very low heat for about 2-3 minutes, just until the cheese is beautifully melted and gooey. Serve it hot and enjoy this delicious, easy meal!