Preheat an oven to 400 degrees. Grease a 10- inch cast-iron pan.
In a large bowl, stir together the cornmeal, flour, baking powder, salt, cayenne, sugar, jalapenos and cheese. Make a well in the center.
In another bowl, whisk together the egg, buttermilk and melted butter until just blended. Pour the egg mixture into the well in the cornmeal mixture and fold gently until the batter is blended and not lumps remain
Spoon the batter into the prepared pan. Bake until a toothpick inserted into the center of the corn break comes out clean, 20-25 minutes. Transfer the pan to a wire rack and let cool for at least 15 minutes before serving. Serves 8 to 10