In a small bowl, sift flour once or twice to remove any clumps and to make it light and soft. Set aside. In a separate medium bowl, gently beat 1 egg until the yolk and egg whites are just barely incorporated. Prepare ice cold water by combining water and ice cubes in a cup. Using a strainer, measure 1 cup of ice cold water and add it to the bowl with the beaten egg. Make sure you do not actually add ice cubes to the tempura batter mixture.