Bring a pot of salted water to a boil. Add potatoes and cook 10 to 12 minutes, until fork tender. Drain and return to hot pot. Add sour cream, milk, and butter, and smash with a potato masher. Season with salt and pepper.
Combine the bread crumbs, cumin, and allspice in a large bowl. Add milk, egg, onion, Worcestershire sauce, tomato paste, parsley, and beef. Mix together and form 4 or 5 oval-shaped patties.
Heat a large nonstick skillet over medium-high heat. Coat with vegetable cooking spray. Add patties to pan and cook 5 minutes. Flip, reduce heat, and cook 10 minutes more or until cooked through. Remove from pan and keep warm.
To make gravy, add butter to pan and melt. Sprinkle in flour and cook over medium heat 2 minutes, whisking. Slowly add broth, stirring until combined. Bring to a boil and cook 2 minutes. Whisk in barbecue sauce and tomato paste. Serve with meatloaf patties and potatoes.