Step 1Blend the sugar and orange zest in a food processor for 20 to 30 seconds. Set aside.
Step 1Heat the oven to 350 degrees. Spray 16 muffin cups with cooking spray and set aside. After chopping the oranges, allow segments to sit for a few minutes, then drain by holding orange in hands and allowing the juice to run off.
Step 2Combine the pastry flour, bread flour, cornmeal, baking powder, baking soda and salt in a large bowl.
Step 3In the bowl of an electric mixer, beat the eggs until light, about 2 minutes. Add the sugar and beat until smooth. Add the melted butter in three parts, beating after each addition.
Step 4In a separate bowl, combine the sour cream and milk. Add to the egg mixture and mix well. Add the orange pieces and zest and gently combine.
Step 5Stir the wet ingredients into the dry until just combined. Do not over-mix.
Step 6Fill the muffin cups evenly with the batter. Place one orange round on top of each muffin, slightly pushing down into batter. Sprinkle each muffin with 1 tablespoon of orange sugar.
Step 7Bake until golden and a cake tester comes out clean, about 20 minutes.