These muffins can be made up to one day ahead and stored in an airtight container at room temperature.

1 1/2 cups all-purpose flour
3/4 cup cornmeal
1/2 cup granulated sugar
1 1/2 teaspoons baking powder
1/2 teaspoon baking soda
1/2 teaspoon ground cinnamon
1/4 teaspoon salt
2 teaspoons finely grated orange zest (optional)
1 1/4 cups low-fat buttermilk, plus about 2 tablespoons for tops
2 large eggs, separated
2 tablespoons unsalted butter, melted
1 1/2 cups blueberries (about 1/2 pound), picked over
2 1/2 teaspoons coarse sanding sugar (optional)
Nonstick cooking spray

Preheat oven to 400, with rack in center. Lightly coat a standard muffin tin with cooking spray. In a medium bowl, whisk together flour, cornmeal, granulated sugar, baking powder, baking soda,     cinnamon, salt, and orange zest, if using.

In a small bowl, whisk together buttermilk, egg yolks, and butter. Stir buttermilk mixture into flour mixture until just blended. In a mixing bowl, whisk the egg whites until just stiff. Gently fold whites and blueberries into the batter until just combined.

Spoon batter into prepared muffin tin, filling each cup three-quarters full. Bake     12 minutes. Remove from oven; gently brush tops with buttermilk, and sprinkle with sanding sugar, if desired. Continue baking until tops are golden and a cake tester inserted in a muffin center comes out clean, 6 to 8 minutes more. Let muffins cool slightly, about 10 minutes, before turning out of tin.