Preheat oven to 400°. Grease 12-cup muffin tin. Mix together dry ingredients. Set aside. Beat together egg, milk and butter or oil and fold into dry ingredients. Batter will be lumpy and fairly thick, but quite moist. Add more milk if necessary. Add blueberries last (do not defrost frozen berries first). Fill muffin cups 2/3 full (or more, for larger muffins) and bake 20 to 30 minutes, or until toothpick inserted into the center comes out clean.