Preheat your oven to 350°F (175°C) and grease a muffin tin with nonstick cooking spray. This will help ensure your mini meatloaf muffins release easily once baked.

In a large mixing bowl, combine the ground beef, minced onion, eggs, breadcrumbs, Worcestershire sauce, pepper, seasoning salt, garlic powder, and 1/2 cup of ketchup. Mix gently with your hands until just combined. Be careful not to overmix, as this can make the meatloaf tough.

Fill each muffin cup in the prepared muffin tin with the meatloaf mixture, pressing it down slightly to ensure they hold their shape.

In a separate bowl, mix the remaining 1/4 cup of ketchup with the brown sugar and mustard. Spoon this mixture on top of each meatloaf muffin for a sweet and tangy glaze.

Bake in the preheated oven for about 30 minutes, or until the meatloaf muffins are fully cooked and reach an internal temperature of 160°F (70°C). A helpful tip: you can check the doneness using a meat thermometer.

Allow the mini meatloaf muffins to cool for a few minutes before serving. This will make them easier to remove from the muffin tin.