Spread these corn muffins with a little butter and jam for a special breakfast or snack.
Adjust oven rack to middle position and heat oven to 375 degrees. Spray 12-cup muffin tin, including top, with vegetable oil spray.
In medium bowl, whisk together flour, cornmeal, baking powder, baking soda, and salt.
In large bowl, whisk sugar and eggs until well combined, light-colored, and thick, about 1 minute. Add sour cream, melted butter, and milk and whisk to combine.
Add flour mixture and use rubber spatula to gently stir until just combined and no dry flour is visible. Do not overmix.
Spray ¼-cup dry measuring cup with vegetable oil spray. Use greased measuring cup to divide batter evenly among muffin cups.
Spray ¼-cup measuring cup with vegetable oil spray.
Scoop batter with greased measuring cup and scrape off any extra batter that is dripping from the bottom or overflowing on top. This ensures that all muffins will be equal in size and that there will be enough batter to fill all muffin tin cups.
Pour batter into muffin tin cup, using a rubber spatula to scrape batter from measuring cup if needed.
Place muffin tin in oven. Bake until muffins are golden brown and toothpick inserted into center of 1 muffin comes out clean, 20 to 25 minutes.