Heat the oven to 375 °F and lightly coat a 2-quart casserole dish with cooking spray. The dish should be ready before the chili is finished so you can assemble while the filling is still hot.

Cook the ground beef and chopped onion in a large skillet until the beef is no longer pink and the onion has softened, then drain off excess grease. The mixture should look browned and savory rather than wet or oily.

Stir in the minced garlic, chili powder, and cumin, and cook briefly for about 30 seconds. You should smell the spices and garlic bloom right away without letting the garlic darken.

Add the crushed tomatoes and frozen corn, then simmer for 5 to 7 minutes. The chili should thicken enough to hold a spoon upright for a second instead of running across the pan.

Take the skillet off the heat and stir in the black beans, then season with salt and pepper to taste. The finished chili should be thick, spoonable, and evenly mixed so it can support the topping.

Whisk the cornmeal, all-purpose flour, salt, sugar, baking powder, and baking soda together in a large bowl. This helps the leavening distribute evenly so the topping bakes up with a uniform crumb.

In a smaller bowl, whisk the milk, eggs, and melted and cooled butter until smooth. The wet mixture should look fully blended with no streaks of egg.

Pour the wet mixture into the dry ingredients and stir just until combined. A few small lumps are fine, and the batter should look thick but easy to spoon.

Transfer the hot chili to the prepared baking dish and spoon the cornbread batter over the top in dollops before gently spreading it. This light touch helps the batter stay on top instead of sinking into the chili.

Bake for 28 to 35 minutes, until the cornbread is lightly golden. A toothpick inserted in the center should come out with moist crumbs, not wet batter.