Preheat your oven to 375°F (190°C) and prepare your loaf pan by greasing it or lining a baking sheet with parchment paper.

In a large mixing bowl, combine ground beef, breadcrumbs, eggs, whole milk, diced onion, minced garlic, Italian seasoning, paprika, salt, and black pepper and mix gently.

Shape two-thirds of the meat mixture into a flat layer in the bottom of the pan, creating a cavity for the mozzarella.

Fill the well with the mozzarella cheese, then cover it completely with the remaining meat mixture and seal the edges.

In a small bowl, whisk together the ketchup, brown sugar, and Worcestershire sauce until smooth and spread it over the meatloaf.

Bake for 45-50 minutes or until the internal temperature reaches 160°F (71°C), tenting with foil if the glaze browns too quickly.

Let the meatloaf rest for 10 minutes before slicing for optimal juiciness.

Slice and serve warm, enjoying the gooey mozzarella core.