Preheat oven to 400 degrees.
Prepare a muffin pan(s) with cupcake/muffin liners in each pocket (this recipe makes about 12 muffins).
Combine the oat milk and apple cider vinegar in a small bowl or cup and set aside to curdle as your "buttermilk".
In a large mixing bowl, whisk together all the dry ingredients (flour, sugar, baking powder, salt, cinnamon and cornstarch). Pour in the oat milk/vinegar mixture, coconut oil and vanilla. Stir gently with a wooden spoon or rubber spatula.
Add in blueberries and gently fold them in until just evenly combined.
Add about 1/4 cup of batter into each muffin liner. Sprinkle the sugar in the raw on top of each and then bake for 22-26 minutes or until a toothpick comes out clean from inserting into the center. Let cool for 5 minutes before removing from the tins and transferring to a cooling rack.
Enjoy for up to 3-4 days!