Preheat oven : to 375°F (190°C). Lightly grease a loaf pan or line with parchment paper.
Make topping : In a small bowl, mix ketchup, brown sugar, and vinegar. Set aside.
Prepare meat mixture : In a large bowl, combine ground beef, breadcrumbs, eggs, milk, diced onion, diced jalapeños, 1 ½ cups shredded cheddar, garlic, Worcestershire, salt, pepper, and paprika. Mix gently until just combined.
Shape loaf : Transfer mixture into the prepared loaf pan or form a free-form loaf on a baking sheet lined with foil.
Add topping : Spread ketchup mixture evenly over the top.
Bake : Place in oven and bake for 45–50 minutes, until internal temperature reaches 160°F (71°C).
Cheesy finish : Remove from oven, sprinkle with remaining cheddar and sliced jalapeños, then return to oven for 5–7 minutes until cheese melts.
Rest u0026 slice : Let loaf rest 10 minutes before slicing to keep it juicy.