Heat the oven to 375°F and grease a 9-by-13-inch dish. Brown beef and onion and drain.
Stir in beans, tomato sauce, molasses, vinegar, Worcestershire, paprika and 1/2 teaspoon salt and simmer 6 minutes. Spread hot filling in the dish.
Whisk cornmeal, flour, baking powder and remaining salt. Whisk egg, milk and butter separately and stir into dry ingredients just until combined.
Spoon batter in small mounds over the filling and spread gently to cover.
Bake for 30 to 35 minutes until the cornbread is golden and tests clean. Rest 10 minutes.