Preheat the oven to 400°F.
Spray a standard 12-cup muffin tin with cooking spray.
In a large bowl, combine the flour, cornmeal, sugar, baking powder, and salt.
In a small bowl, combine the milk, eggs, and cooled melted butter.
Add the wet ingredients to the dry ingredients and mix just until the dry ingredients have been moistened (it's okay if there are some lumps). Don't overmix, as this can cause your muffins to be dense, tough or too crumbly.
Divide the batter evenly among the 12 muffin cups (each one should be about 2/3 full).
Bake for 15 to 20 minutes or until a toothpick inserted in the center comes out clean.
Place the pan on a wire rack and allow the muffins to cool for a few minutes before removing them from the pan. These are best when served warm!