Preheat your oven to 190°C (375°F). Lightly grease a 9x13 inch (23x33 cm) baking dish.

In a large skillet or Dutch oven over medium-high heat, add the ground beef. Break it up with a spoon and cook until browned, about 7-10 minutes. Drain off any excess grease.

Add the chopped yellow onion and green bell pepper to the skillet with the browned beef. Cook, stirring occasionally, until the vegetables have softened, about 5-7 minutes.

Stir in the minced garlic and cook for another minute until fragrant. Be careful not to burn the garlic.

Add the ketchup, Worcestershire sauce, brown sugar, yellow mustard, chili powder, 1 tsp salt, and 1/2 tsp black pepper to the skillet. Stir well to combine.

Pour in the 120ml (1/2 cup) of water and bring the mixture to a simmer. Reduce the heat to low, cover, and let it cook for at least 10 minutes to allow the flavors to meld. This creates the rich Sloppy Joe sauce.

While the Sloppy Joe mixture is simmering, prepare the cornbread topping. In a medium bowl, whisk together the cornmeal, all-purpose flour, granulated sugar, baking powder, and 1/2 tsp salt.

In a separate small bowl, whisk together the egg and 240ml (1 cup) milk.

Pour the wet ingredients (milk and egg mixture) into the dry ingredients (cornmeal mixture). Add the 55g (4 tbsp) of melted butter. Stir until just combined. Do not overmix; a few lumps are okay.

Pour the prepared Sloppy Joe meat mixture evenly into the bottom of the prepared baking dish.

Carefully spoon the cornbread batter over the Sloppy Joe mixture, spreading it gently to cover the entire surface. You can create swirls with a knife if desired, but ensure it's mostly covered.

Bake in the preheated oven for 25-30 minutes, or until the cornbread is golden brown and a toothpick inserted into the center comes out clean. The filling should be bubbling around the edges.

Let the casserole rest for 5-10 minutes before serving. This allows the filling to set slightly and makes it easier to serve.