1½ cups sugar
1 cup water
½ cup unsweetened cocoa (preferably
Dutch process)
1 teaspoon vanilla syrup
4 tablespoons milk
6 cups vanilla ice cream
Stir sugar and water in heavy medium saucepan over medium-low heat until sugar dissolves. Increase heat and bring to boil. Place cocoa in small bowl. Gradually whisk in sugar syrup. Return mixture to same saucepan. Boil 1 minute, whisking constantly. Pour into bowl, Whisk in vanilla and cool completely. Cover and chill until cold, at least 1 hour. (Syrup can be made 1 week ahead. Keep refrigerated.)
Pour 3 tablespoons chocolate syrup and 1 tablespoon milk into blender. Add 1 ½ cups ice cream and blend until smooth. Pour into glass. Repeat in 3 more batches, using the same amounts each time. 4 servings.