Place 1/2 cup milk and 3 tablespoons malt powder in the jar of a blender, and process until malt is dissolved. Add half the vanilla ice cream, and blend until smooth. With the motor running, add remaining vanilla ice cream, 1 scoop at a time, until it is fully incorporated. Pour half the shake into a glass measuring cup, and place in freezer. Divide remaining half between two glasses, and place glasses in freezer. Allow to chill for 10 minutes before proceeding to step two.
Place remaining 1/2 cup milk and remaining 3 tablespoons malt powder in clean jar of blender, and process until malt is dissolved. Add half the chocolate, or strawberry, ice cream, and blend until smooth. With motor running, add remaining ice cream, one scoop at a time, until fully incorporated. Divide half the shake between two empty glasses, and top off the two partially filled glasses from freezer with the remainder. Allow the half-filled glasses to freeze for 10 minutes. Stir reserved vanilla shake before topping off remaining glasses. Garnish with malted-milk powder and malted-milk balls if desired, and serve immediately.