Preheat oven to 425 degrees. Spray muffin tin with baking spray or line with muffin papers.
Prepare the Batter
In a large bowl, mix together the all-purpose flour, granulated sugar, baking soda, salt, and ground cinnamon.
Place the sourdough starter in another bowl along with the whole milk, vegetable oil, and large egg. Mix together with a fork or dough whisk to combine. Blend the sourdough into the flour mixture, until thoroughly combined.
Gently fold in the fresh or frozen blueberries just until blended.Try not to overmix the muffin batter to avoid coneheads that might develop during baking, or a tough crumb.
Bake the Muffins
Spoon batter into the prepared muffin cups, filling two-thirds full. If desired, sprinkle with decorator sugar or Demerara sugar.
Bake in preheated oven for 15-20 minutes, until lightly browned. Remove from oven and allow to set for 5 minutes before placing on a wire rack to cool completely.
Serve with butter or honey butter for brunch or a morning snack.
Store in a covered container for up to 3 days, or freeze in a plastic freezer bag for up to 2 months. This recipe will serve 10-12 people.