1. Center a rack in the oven and preheat the oven to 400 degrees F. Butter or spray the 12 molds in a regular-size muffin pan or fit the molds with paper muffin cups.
2. In a large mixing bowl, whisk together the flour, cornmeal, sugar, baking powder, baking soda, salt, chili powder and black pepper. In a large measuring cup or another bowl, whisk the buttermilk, melted butter and egg yolk together until well blended. Pour the liquid ingredients over the dry ingredients and, with the whisk or a rubber spatula, gently but quickly stir to blend. The batter should be lumpy. Stir in the corn kernels, jalapeño and red pepper. Divide the batter evenly among the muffin cups.
3. Bake for about 20 minutes, or until the tops are golden and a thin knife inserted into the center of the muffins comes out clean. Transfer the pan to a rack and cool for 5 minutes before removing each muffin to finish cooling.