Preheat oven to 400°F. Prepare the muffin pan by greasing the cups or lining them with papers, then spraying the papers with non-stick baking spray; this helps release the muffins from the papers., Whisk together the flour and sugar., In a separate bowl, whisk together the milk, oil, eggs, and vanilla. Add to the dry ingredients, stirring until the flour is moistened; it will be a bit lumpy., Quickly and gently stir in the blueberries., Fill the muffin cups 3/4 full; sprinkle muffins with sugar, if you like., Bake the muffins for 20 to 25 minutes, or until they're golden brown and a cake tester or toothpick inserted into the center comes out clean., Remove the muffins from the oven, and allow them to cool for 3 to 5 minutes in the pan. Remove them from the pan and serve warm or at room temperature. Wrap airtight and store at room temperature for several days; freeze for longer storage.