Preheat oven to 375°F (190°C).
In a large mixing bowl, combine ground beef, breadcrumbs, egg, milk, onion, garlic, Worcestershire sauce, salt, and pepper. Mix by hand until just combined.
Shape the meat mixture into a 9x5 inch loaf and place it in the center of a large rimmed baking sheet or roasting pan.
In a separate bowl, toss cubed potatoes with olive oil, rosemary, and a pinch of salt and pepper.
Spread the potatoes in a single layer around the meatloaf on the baking sheet.
In a small bowl, whisk together the BBQ sauce, ketchup, and brown sugar.
Brush half of the BBQ glaze over the top and sides of the meatloaf.
Bake for 45 minutes in the preheated oven.
Remove from oven and brush the remaining glaze over the meatloaf. Stir the potatoes to ensure even browning.
Bake for an additional 15 to 20 minutes until the internal temperature of the meatloaf reaches 160°F (71°C) and potatoes are fork-tender.
Let the meatloaf rest for 10 minutes before slicing to retain juices.