Preheat oven to 375°.
Lightly spoon flour into dry measuring cups; level with a knife. Combine flour, granulated sugar, cornmeal, baking powder, and salt in a medium bowl, stirring with a whisk. Make a well in center of mixture. Combine yogurt, melted butter, milk, and egg, stirring with a whisk; add to flour mixture, stirring just until moist.
Place 12 paper muffin cup liners in muffin cups. Divide the batter evenly among cups. Sprinkle batter evenly with turbinado sugar, if desired. Bake at 375° for 20 minutes or until a wooden pick inserted in center comes out clean. Cool on a wire rack.