Preheat the oven to 350°F. Line 24 regular sized muffin tins with paper liners. Spray the liners with nonstick cooking spray.
In a large bowl, whisk together the cornmeal, flour, sugar, baking powder, and salt.
In a medium bowl, whisk together the melted butter, eggs, sour cream, and milk. Pour this mixture into the cornmeal mixture, and stir with a wooden spoon until just blended (you should still see faint streaks of the cornmeal mixture, and it will be lumpy).
Add the pepper jack and jalapeno to the batter, (or skip one or the other) and stir just until blended. Fill the muffin cups ¾ of the way with the batter.
Bake for 20 to 25 minutes, until a toothpick inserted in the center comes out clean. Let cool in the pan on a wire rack for 10 minutes, then turn the muffins out of the pan, and let them finish cooling upright in just the paper liners on the wire rack. Serve warm or at room temperature.
Fork in the Road
Optional add-ins for nine muffins (half the batch):