Pour milk into a 12-ounce highball glass. Add the seltzer and stir vigorously so that a white head forms on top of the milk and comes just to the top of the glass. Slowly drizzle the chocolate syrup into the milk, letting it fall gently to the bottom of the glass, and stir, using a long slender spoon, so as to just mix the chocolate into the milk but trying not to disturb the white head on the top of the beverage. Serve immediately.
Yield: 1 serving