Preheat oven to 425°F.  Grease a muffin pan with 2+1/2-inch diameter cups, or line with paper baking cup liners; set aside. In a bowl, sift together flour, sugar, baking powder and salt; add frozen blueberries, and make a well in the center. Pour the milk into a 2 cup glass measure and add egg and butter; blend well. Pour liquid all at once into flour well. (This method allows you to mix the batter with fewer strokes, avoiding overtiring.) Making 12 to 15 full circular strokes that scrape the bottom of bowl; stir just until dry ingredients are moistened. Batter 'should' be lumpy. Fill each prepared muffin cup 2/3 full with batter. Bake for 20 to 25 minutes or until tops are lightly browned. Remove muffins from pan immediately  Makes 12.