Preheat your oven to 400°F (200°C). Line the baking sheet with parchment paper for easy cleanup, if desired.
In a mixing bowl, combine ground beef, breadcrumbs, milk, ketchup, egg, onion, Worcestershire sauce, garlic powder, salt, and pepper. Mix well until all ingredients are fully integrated.
Shape the meat mixture into 8 small loaves and place them on one side of the prepared baking sheet.
In another bowl, toss the halved baby potatoes with olive oil, garlic powder, rosemary, salt, and pepper until evenly coated. Spread the potatoes on the other side of the baking sheet.
Bake in the preheated oven for 25-30 minutes, or until the mini meatloaves are cooked through (internal temperature should reach 160°F/70°C) and the potatoes are golden and tender.
If desired, brush additional ketchup over the meatloaves in the last 5 minutes of cooking for added flavor.
Remove the baking sheet from the oven and let it rest for a few minutes before serving.