Preheat your oven to 375°F (190°C). Grease an 8-inch square baking dish or a similar-sized casserole dish with butter.

1. Combine the dry ingredients.In a large mixing bowl, whisk together the cornmeal, flour, baking powder, sugar, salt, and black pepper until evenly combined.
2. Mix the wet ingredients.In a separate bowl, whisk the buttermilk, eggs, and melted butter. Add the sour cream if you’re using it, and mix until smooth.
3. Make the batter.Pour the wet ingredients into the dry mixture. Stir gently until just combined. Avoid overmixing, as this can make the cornbread dense.
4. Add the cheese and vegetables.Fold in the shredded cheddar, diced jalapeños, and corn kernels. Make sure the ingredients are distributed throughout the batter for a flavorful bite in every piece.
5. Transfer to the baking dish.Spread the batter evenly in the prepared dish. Sprinkle the extra cheddar cheese over the top and arrange a few jalapeño slices on top if desired.
6. Bake until golden.Place the dish in the preheated oven and bake for 25–35 minutes, or until the top is golden brown and a toothpick inserted into the center comes out clean or with a few moist crumbs.
7. Let it rest.Remove the cornbread bake from the oven and allow it to cool for 5–10 minutes before slicing. This helps the center set and makes serving easier.
8. Serve and enjoy.Cut into squares and serve warm alongside chili, barbecue chicken, grilled meats, soups, or your favorite comfort-food dinner.