Preheat oven to 375°F. Spray 12 standard size muffin-pan cups with vegetable cooking spray or use paper cupcake cups. Mix together flour, sugar, baking powder and salt. Mix together milk, oil, apple sauce, egg and vanilla. Make a well in the center of flour mixture. Add milk mixture all at once to well, tossing with a fork until dry ingredients are just moistened. DO NOT OVER MIX. Fold in blueberries. Spoon batter into prepared pan, filling cups 2/3 full. Bake muffins until tops are firm and golden brown, 20 to 25 minutes. Transfer pan to a wire rack to cool slightly. Turn muffins out onto rack to cool completely.