In a large bowl, whisk together the flour, cornmeal, sugar, baking powder, baking soda, and salt.
In a medium bowl, whisk together the buttermilk, egg, and butter. Pour into the flour mixture and stir just until incorporated. If the batter seems too thick to pour, add a little more buttermilk. (I did not need to add any.)
Spray a nonstick skillet or griddle with cooking spray and heat over medium heat (about 300°F).
When hot, pour ⅓ cup of batter into the skillet. Spread the batter out more, if necessary, to about a 4-inch diameter.
Working in batches, being careful not to overcrowd the pan, cook the pancakes for 3-4 minutes, or until the bubbles begin popping on top and they are golden brown.
Gently, but quickly, flip over the pancakes. Cook an additional 3-4 minutes until the other side is also golden brown.
Before the next batch, wipe out the pan with a paper towel and repeat with the remaining pancake batter.
Serve warm, topped with maple syrup.