Preheat your oven to 360°F. Place a 10-inch cast iron skillet in the oven to heat while you prepare the batter.
In a large bowl, combine the flour, cornmeal, baking powder, and salt.
In a second large bowl, whisk together the buttermilk, melted butter, and eggs until well combined.
Gradually add the dry ingredients to the wet ingredients, stirring until combined. Do not overmix.
Fold in the shredded cheese, chopped jalapeños, and corn kernels until evenly distributed.
Carefully remove the hot cast iron skillet from the oven. Add the two tablespoons of butter to the skillet and let it melt, swirling to coat the bottom and sides of the skillet.
Pour the cornbread batter into the skillet, spreading it evenly.
Place the skillet back in the oven and bake for 20-25 minutes, until the top is golden brown and a toothpick inserted into the center comes clean.
Allow the cornbread to cool in the skillet for 10 minutes before slicing and serving.
Notes
If you prefer a milder cornbread, remove the membranes and seeds from the jalapeños, and for more heat, leave them intact. If you don't have buttermilk, add one tablespoon of lemon juice or white vinegar to 1 cup of milk and let it sit for 5-10 minutes before using.Do not overmix the batter; doing so will result in dense, tough cornbread. Mix just until the ingredients are combined.You can use fresh corn kernels, canned (drained well), or frozen (thawed and drained well).You can use a store-bought cornbread mix, such as (2 x 8.5oz boxes of Jiffy cornbread mix)