Note: This makes 12 cupcakes using a Texas Muffin pan (extra large).
Preheat oven to 350° F.
Line the Texas muffin pan. If you don't have liners large enough, spray the pan with cooking spray to help the homemade liners form to pan. Make your own liners using parchment paper.
In a medium bowl to set aside, add cake flour, baking soda, baking powder and salt. Combine and set aside.
In an electric mixer bowl, whip the granulated sugar and butter together using the paddle attachment until a fluffy texture is formed.
Add to the mixture the eggs one at a time. Add the egg whites and then mix in the vanilla extract.
Using a liquid measuring cup, add the buttermilk. In the same measuring cup, add the sour cream and whisk until combined.
Alternate adding the flour mixture and the buttermilk mixture to the electric mixer. Begin with about 1/3 of the flour mixture, add 1/3 buttermilk mixture, continue until combined.
In a separate bowl add the fresh blueberries and coat with cake flour (this assists in keeping the blueberries from sinking) - do not skip this step!
Using a spatula, gently fold in the fresh blueberries coated in cake flour.
Fill the 6 paper or parchment lined Texas muffin cups about ⅓ of the way to the top.
Bake for approximately 35 minutes (ovens vary) or until it passes the toothpick test (insert toothpick into center and the toothpick should come out clean).
Let them cool in muffin pan for 5 minutes prior to transferring to a cooling rack to cool completely before frosting.