Preheat oven to 375°F (190°C) and line or grease a muffin tin
Whisk flour, cornmeal, sugar, baking powder, and salt in a large bowl
In another bowl, whisk melted butter, eggs, milk, sour cream, and vanilla
Add wet ingredients to dry ingredients and gently fold until just combined
Divide batter evenly into muffin cups, filling about ¾ full
Bake until tops are lightly golden and a toothpick comes out clean
Cool briefly, then transfer to a wire rack and serve