Chill a metal bowl or pitcher in the freezer for 5–10 minutes (optional)
Add 2–4 tablespoons cold milk (or dairy-free milk) to a blender cup or frother container
Add 1–2 tablespoons sweetener (optional) such as sugar, simple syrup, or vanilla syrup
Add 1–2 teaspoons vanilla extract (optional)
Add ice (optional, if you want it thicker)
Froth with a handheld milk frother for 30–60 seconds (or until thick and foamy)
Or blend in a blender on high for 20–30 seconds (or until thick)
Spoon or pour the cold foam onto your cold coffee or espresso drink immediately