Set oven to 375 degrees.
In the KitchenAide mixer, combine butter, sugar, and eggs. Mix till it is a smooth mixture.
Add in vanilla and fed sourdough starter to the wet ingredients, combining all together.
In a separate bowl, add in flour, baking powder, baking soda, salt, arrowroot powder, and cinnamon.
Once wet ingredients are mixed all together, slowly add in the dry ingredients to it. Pour in the milk to make the dough less thick.
Add in blueberries mixing slow so you do not crush the blueberries.
Put liners in the muffin pan and scoop out the dough into the liners. I will fill my liners up with dough about 3/4 of the way.
Bake in oven for 20-25 minutes.