Bring a large pot of salted water to a boil. Add pasta and cook according to package directions until al dente. Drain and set aside, reserving 1 cup of pasta water.

In a large skillet over medium-high heat, cook bacon strips until crispy, about 8-10 minutes. Remove bacon to a paper towel-lined plate and chop once cooled. Reserve 2 tablespoons of bacon fat in the skillet.

Add ground beef to the same skillet with bacon fat. Brown the meat over medium-high heat, breaking it apart as it cooks, about 5-7 minutes. Drain excess fat if needed, leaving about 2 tablespoons. Season with salt and pepper.

Add sliced onion and minced garlic to the beef. Cook for 3-4 minutes, stirring frequently, until the onion softens and becomes translucent.

Add butter to the skillet and let it melt completely. Sprinkle flour over the butter and stir constantly for 2 minutes to create a roux base.

Slowly pour in heavy cream while whisking constantly to avoid lumps. Add beef broth and stir until well combined. Let the mixture simmer for 3-4 minutes until it thickens slightly.

Remove the skillet from heat and stir in American cheese slices until completely melted and smooth. Add grated Parmesan cheese and mix thoroughly. Taste and adjust seasoning as needed.

Add cooked pasta to the sauce and toss gently to coat every strand. If the mixture seems too thick, add reserved pasta water a little at a time until you reach desired consistency.

Top each serving with chopped crispy bacon, fresh lettuce, sliced tomato, and extra Parmesan cheese if desired. Serve immediately.