Adjust oven rack to middle position and heat oven to 400 degrees. Spray muffin tin with nonstick spray.
STEP 2
Whisk flour, cornmeal, baking powder, baking soda, and salt in a bowl; set aside. In another bowl, whisk eggs until light-colored, about 20 seconds. Add sugar to eggs; whisk until thick, about 30 seconds. Add melted butter gradually, whisking until combined. Mix in half the sour cream and half the milk, then the remaining sour cream and milk until combined.
STEP 3
Add wet ingredients to dry ingredients and mix gently until just combined. Do not over-mix. Divide batter evenly among muffin cups to form mounds.
STEP 4
Bake until muffins are golden brown and a skewer inserted comes out clean, about 18 minutes. Cool in tin for 5 minutes, then invert onto a wire rack, standing muffins upright to cool for an additional 5 minutes.