1. Combine 3 cups water and espresso powder. Pour espresso into 2 ice cube trays; freeze 4 hours or until firm.
2. Place 4 frozen coffee cubes, chocolate milk, and 1 1/2 teaspoons chocolate syrup in a blender; process until slushy. Pour slush into a glass; swirl 1 1/2 teaspoons chocolate syrup into the slush. Serve immediately.