Adjust oven rack to upper-middle position and heat oven to 425 degrees. Grease a 12-cup muffin tin (I used baking spray). In medium-sized bowl, whisk together 1 1/2 cups cornmeal, flour, baking powder, baking soda, and salt.
Combine the milk and remaining 1/2 cup cornmeal in large bowl. Microwave the mixture for 1 1/2 minutes. Whisk thoroughly and continue to microwave in 30 second increments, whisking every time, until thickened to a batter-like consistency, 1 to 3 minutes.
Whisk in the sour cream, melted butter, and sugar until evenly combined, then whisk in the eggs. Fold in flour mixture until evenly combined. Using a measuring scoop or large spoon, divide the batter evenly into the prepared muffin tin (about 1/2 cup batter per cup).
Bake until tops are golden brown and toothpick inserted in center comes out clean, 13 to 17 minutes, rotating muffin tin halfway through baking. Let the muffins cool on wire rack for 5 minutes, then remove the muffins from the muffin tin and cool 5 minutes longer. Serve warm.