Pre-heat oven to 375F/190C. Place muffin liners in muffin tin. Keep aside.Sift or whisk, flour with baking powder, baking soda, and salt. Keep aside.Gently mix the blueberries with cornstarch until the blueberries are coated well. Keep aside.In a mixing bowl, add the sugar, oil, vanilla, egg, and beat until sugar dissolves.Add the buttermilk to the wet ingredients and beat until combined.Add the flour and mix gently, then add the blueberries and gently fold into the batter.Scoop the batter in muffin liners. This batter will make 8 to 9 medium size muffins.Bake for 15 to 20 minutes or until a toothpick inserted in the middle of the muffin comes out clean.