Blueberry-Cornmeal Muffins

INGREDIENTS

• 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
• 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 and rinsed
• 2 1/2 teaspoons coarse sanding sugar (optional)
• Nonstick cooking spray