Combine the heavy cream, milk, sweetener, and vanilla extract (if using) in a mason jar or a medium-sized bowl.

If using a mason jar, secure the lid tightly. If using a bowl, have your frothing tool ready.

For a mason jar: Shake vigorously for 30-60 seconds, or until the mixture is thick and frothy. You'll see it increase in volume.

For a bowl: Use a handheld milk frother and whisk the mixture for about 30-60 seconds, or until it forms stiff peaks and is bubbly and voluminous. Alternatively, you can use a French press: Pour the mixture into the French press carafe and pump the plunger up and down vigorously for about 45-60 seconds until frothy.

Once frothed, spoon the cold foam generously over your favorite iced coffee, cold brew, or other chilled beverage.

Enjoy immediately while it's perfectly frothy!