Preheat your oven to 350˚F.
For best results, have all your ingredients at room temperature.
To a medium bowl, add your sourdough starter, the egg, the melted butter, and the vanilla extract.
Using a whisk, mix all the ingredients until the butter is well incorporated.
To this bowl, add the gluten-free flour, coconut sugar, baking soda, and salt.
Using your whisk, mix this mixture until all the ingredients all well incorporated.
Add the blueberries and gently fold them into the muffin batter.
Line your muffin tin with the paper cupcake liners.
Fill the paper cups only ⅔ to ¾ since the muffins will rise.
Bake them in your preheated oven at 350˚F for 20-30 minutes or until golden brown and an inserted knife or toothpick comes out clean.
Take the muffins out of the tin in their paper cups and let them cool on a cooling rack.
Pro tip: these gluten-free sourdough blueberry muffins taste even better the next day - if you can wait that long ...