Preheat oven to 375 degrees F. Prepare muffin tin with 12 cupcake liners. If you're not using cupcake liners, lightly spray with cooking spray.

In a medium bowl, combine gluten free flour blend, guar gum, sugar, baking powder, baking soda, salt and lemon zest.

In a large measuring cup or bowl, combine beaten egg, buttermilk, oil and extract.

Pour the liquid buttermilk mixture into the flour and stir until just combined. The batter should be dense but smooth.

Gently fold in blueberries until just combined. Transfer batter between 12 standard muffin cups. Each one should fill almost to the top. Sprinkle the top with raw sugar if desired.

Bake for 18-20 minutes, or until golden brown on the top.