Heat oil in 12“ skillet or 10” deep dish skillet until shimmering. Add the onion, chili powder, and salt and cook until the onion is softened, about 5 min. Stir in the garlic and cook until fragrant, about 30 sec.
Stir in the ground sirloin, beans, and tomatoes, and bring to a simmer, breaking up the meat, about 5 min. Stir the cheddar and cilantro into the filling and season with salt and pepper to taste.
Whisk the flour, cornmeal, sugar, baking powder, baking soda, and salt together in a bowl. In a separate small bowl or measuring cup whisk the buttermilk and egg together. Stir the buttermilk mixture into the flour mixture until uniform. Stir in the butter until just combined.
Dollop the cornbread batter evenly over the filling and spread into an even layer. Bake until the cornbread is cooked through in the center, approximately 15 min. Serve.
Serves: 6 Total cook time: 26min
Source: Cook's Illustrated 10/06