Preheat the oven to 350°F (175°C). Grease a 9x13-inch baking dish and set aside.
In a medium bowl, combine the ketchup and barbecue sauce until evenly blended. Reserve for later use.
Place the lean ground beef into a large mixing bowl. Crush the crackers in a sealed plastic bag using a rolling pin, then add the crumbs to the beef.
Incorporate the dry onion soup mix and crack the eggs directly into the bowl. Add ½ cup of the prepared ketchup-barbecue mixture.
Using clean hands, knead the ingredients together until fully integrated. Press this mixture evenly into the greased baking dish to form the meatloaf base.
Spread the remaining ketchup-barbecue sauce mixture across the top of the meatloaf layer.
Bake the meatloaf uncovered for 30 minutes.
While the meatloaf is baking, cook the elbow macaroni according to the instructions on the package. Drain thoroughly.
In a large bowl, whisk together the milk and condensed cheddar soup until smooth and free of lumps.
Add the salt, pepper, garlic, and onion powder into the mixture, whisking again until incorporated.
Stir the drained macaroni into the sauce, coating all noodles evenly. Mix in 2 cups of the shredded cheese blend until well distributed.
Once the meatloaf has finished its initial bake, remove it from the oven. Spoon the macaroni mixture over the meatloaf and spread it out evenly.
Sprinkle the remaining 2 cups of shredded cheese across the surface.
Return the casserole to the oven and bake for an additional 17–20 minutes, or until the cheese topping is melted and beginning to brown.
Allow the dish to rest for a few minutes before slicing and serving.