Pour the chilled heavy cream, 2% milk, and vanilla syrup into a tall, narrow glass or frothing pitcher.
Add the vanilla whey protein powder on top of the liquid.
Insert a handheld milk frother at a 45-degree angle just below the surface of the liquid.
Whisk for 45 to 60 seconds, moving the frother up and down slightly, until the mixture doubles in volume and reaches a thick, pourable consistency similar to melted soft-serve ice cream.
Pour the foam immediately over cold brew or iced coffee to allow for the characteristic slow-cascading effect.