Preheat your oven to 375°F and lightly grease a 9×13-inch baking dish with nonstick cooking spray. Set aside.
In a large mixing bowl, combine the ground meat, chopped onion, minced garlic, breadcrumbs, Worcestershire sauce, beaten egg, cottage cheese, and BBQ sauce. Mix until well combined.
Press the meat mixture evenly into the prepared baking dish to form the meatloaf layer. Place it in the oven and bake for 30 minutes.
While the meatloaf is baking, add the diced potatoes to a pot and cover them with water. Cook over medium heat until the potatoes are tender.
Drain the potatoes, then add the butter to the pot. Use a hand mixer to mash the potatoes until smooth. Add the sour cream, warm milk, salt, and pepper, and mix again until creamy.
After the meatloaf has baked, remove it from the oven and carefully pour off any excess grease.
Spread the mashed potatoes evenly over the meatloaf layer. Top with shredded cheddar cheese and crumbled bacon.
Return the dish to the oven and bake for an additional 15 minutes, or until the potatoes are warmed through and the cheese has melted.
Remove from the oven and serve the casserole hot with your favorite side dishes.