Place heavy cream, milk, and vanilla syrup into a tall carafe with a wide opening.
Stir mixture together.
With an electric milk frother, froth the mixture using an up and down motion until the liquid doubles in volume (at least) and is foamy throughout.
Spoon or pour the foam over your favorite iced coffee.
Notes
Refrigerate in an airtight container and use within 24 hours. Using a lower fat milk is consistent with Starbucks (they use nonfat milk), but I had equal success using 2% and even whole milk. Making sweet cream cold foam at home can be challenging. I have experimented with aerating the mixture using a blender, food processor, immersion blender, French press, hand (manual) frothing whisk and a nitrous oxide whipped cream dispenser. The electric milk frother is fast and the most effective. Using a French press and a nitrous oxide whipped cream dispenser are also workable. Whisking by hand can be effective but is labor intensive. Using blender type appliances does not produce a foam. All ingredients should be as cold as possible for the best success.This is a sweetened cold foam and is delicious stirred into a black coffee drink or added to any of your favorite iced beverages. You can substitute the vanilla syrup for other flavored syrups, or omit the syrup for an unsweetened cold foam.Use store bought vanilla syrup or make your own by adding vanilla extract to homemade simple syrup.