Preheat the oven to 375°F (190°C) and grease a 12-cup muffin tin or line it with paper liners for easier cleanup.

In a small bowl, combine 1/2 cup breadcrumbs with 1/3 cup milk. Let the mixture soak for about 5 minutes so it helps keep the meatloaf bites tender and moist.

In a large mixing bowl, add 1 lb ground beef, the soaked breadcrumbs, 1 large egg, 1/2 small grated or minced onion, 2 minced garlic cloves, 1 teaspoon Worcestershire sauce, 1 teaspoon salt, 1/2 teaspoon black pepper, 1/2 teaspoon smoked paprika (if using), 1 teaspoon dried Italian seasoning, and 1/3 cup grated Parmesan cheese. Mix gently with your hands until just combined, being careful not to overwork the meat.

Scoop about 2 tablespoons of the meat mixture into each muffin cup. Create a small well in the center of each and add roughly 1 tablespoon of shredded mozzarella cheese. Top with another spoonful of meat mixture to seal the cheese inside.

In a separate small bowl, mix together 1/2 cup ketchup, 2 tablespoons brown sugar, and 1 teaspoon mustard. Lightly spread this tangy-sweet glaze over each filled muffin cup.

Bake the meatloaf bites in the preheated oven for 20-25 minutes, or until the meat is cooked through and reaches an internal temperature of 160°F (71°C).

Remove from the oven and serve immediately with your favorite sides, such as creamy mashed potatoes, egg noodles, a crisp green salad, or roasted vegetables.