Heat 1 tablespoon oil in a large pot over medium heat. Add the onion and cook until softened, about 5 minutes. Stir in the garlic and half the diced jalapeño and cook for 1 minute more.

Add the chili powder and cumin. Stir for 30 seconds until fragrant, then pour in the diced tomatoes with their juices and the drained black beans. Season with salt and pepper.

Bring the mixture to a simmer, then reduce the heat and cook uncovered for 15 minutes, stirring occasionally, until the chili thickens slightly.

While the chili simmers, preheat the oven to 400°F and lightly oil an 8-inch square baking pan. In a bowl, whisk together the cornmeal, flour, baking powder, and a pinch of salt.

In another bowl, whisk the milk, egg, and remaining 1 tablespoon oil. Stir in the remaining diced jalapeño. Pour the wet mixture into the dry ingredients and stir just until combined.

Spread the batter into the prepared pan and bake for 18-20 minutes, until the top is golden and a toothpick comes out clean. Let it cool for a few minutes, then cut into squares.

Place a piece of warm cornbread on each plate and spoon the black bean chili generously over the top.