Preheat the oven to 400 degrees F and spray a 12-count muffin pan with nonstick spray and set aside. (You can also line the muffin pan with parchment liners for easy removal.)
In a large bowl, whisk together the flour, cornmeal, baking powder, baking soda, and salt and set aside.
In a medium bowl, beat together the eggs, buttermilk, cooled butter, and sugar.
Then mix in the sour cream.
Add the wet ingredients to the dry ingredients, mixing just until combined.
Fold in 1 cup of the blueberries.
Use a ¼ cup measuring cup to measure the batter out into the muffin tin.
Top the muffins with the remaining blueberries and coarse sugar and bake for 15 to 20 minutes until a toothpick comes clean when inserted into the center of the muffins and the tops spring back slightly when touched.
Allow the muffins to cool in the pan for 10 minutes before running a knife gently around the edge to loosen and remove them.