Bring a large pot of salted water to a boil. Cook elbow macaroni 2 minutes less than package directions until just shy of al dente. Drain and set aside.

In the same pot, melt butter over medium heat. Whisk in flour and cook 1 minute until foamy. Slowly whisk in milk and cook 2-3 minutes until thickened enough to coat the back of a spoon. Remove from heat and stir in 6 oz of the cheddar until smooth. Fold in the cooked macaroni.

Preheat oven to 350F. In a large bowl, combine ground beef, onion, garlic, breadcrumbs, egg, Worcestershire sauce, salt, and pepper. Use your hands to mix until just combined - do not overwork or the meatloaf will be dense.

Press half the meat mixture into the bottom and up the sides of a 9x5-inch loaf pan, creating a well in the center. Fill with the mac and cheese, then top with remaining meat mixture, sealing the edges completely. Spread ketchup over the top.

Bake 45-50 minutes until the internal temperature reaches 160F and the top is caramelized. Sprinkle remaining 2 oz cheddar over the top and bake 5 minutes more until melted and bubbly.

Let rest 10 minutes before slicing - this keeps the mac and cheese center from oozing out. Slice with a serrated knife using a gentle sawing motion.