Preheat the oven to 350°F (175°C). Grease a 9-by-9-inch (23-by-23-cm) baking dish with butter or cooking spray.
In a large bowl, whisk together the cornmeal, flour, sugar, baking soda, and kosher salt.
In a separate bowl, whisk the egg and buttermilk together. Stir in the corn kernels. Pour this wet mixture into the dry ingredients and stir until just combined. Fold in the melted butter.
Spread the batter evenly into the prepared baking dish. Bake for 30 to 35 minutes, until the top is golden brown and a toothpick inserted in the center comes out clean. Leave the oven on.
While the cornbread bakes, cook the ground beef, chopped onion, and bell pepper in a large skillet over medium heat. Break the meat apart and cook until browned and the beef reaches a safe internal temperature of 160°F (71°C). Drain any excess grease.
Stir the black beans and taco seasoning into the beef mixture. Pour in the enchilada sauce and simmer for 5 minutes until the mixture thickens slightly. Keep warm over low heat.
Remove the baked cornbread from the oven. Use a fork to poke holes all over the top of the cornbread.
Spoon the warm beef mixture evenly over the cornbread layer. Sprinkle the shredded cheddar cheese across the top.
Return the casserole to the oven and bake for 15 minutes, or until the cheese is melted and bubbly. Let the dish rest for 10 minutes before slicing and serving.