Preheat the oven to 350 °F. Lightly coat a 12-cup muffin tin with cooking spray.
In a large bowl whisk together flour, cornmeal, sugar substitute, baking powder, baking soda, and salt.
In another mixing bowl beat the butter with an electric mixer on high speed for 3 minutes or until light and fluffy. Add egg and beat another minute. Beat in buttermilk and vanilla until well combined.
Add flour mixture to wet mixture in two batches, beating on medium speed just until combined. Do not over beat. Stir in blueberries.
Scoop batter into prepared muffin tin and bake for 20 to 25 minutes or until a toothpick inserted in the center of a muffin comes out clean.
Cool for 5 minutes, loosen edges, and turn out onto a wire rack to cool completely.
*Gluten-Free Flour Blend
Combine 2 cups rice flour, 2/3 cup potato starch, 1/3 cup tapioca flour and 1 teaspoon xanthan gum.
Store in container with tight-fitting lid; stir before using.
Makes 3 cups.