Line 12 muffin cups with paper liners. In the bowl of an electric mixer fitted with a paddle attachment, mix the flour, sugar, cornmeal, baking powder, and salt. In a separate bowl, combine the milk, melted butter, and eggs. With the mixer on the lowest speed, pour the wet ingredients into the dry ones and stir until they are just blended. Spoon the batter into the paper liners, filling each one to the top. Bake for 30 minutes, until the tops are crisp and a toothpick comes out clean. Cool slightly and remove from the pan.