Combine the heavy whipping cream, whole milk, strawberry syrup (or puree and sugar), and vanilla extract in a deep, narrow container, such as a large mason jar or a tall mixing bowl.
If using a mason jar, secure the lid tightly. If using a bowl, use an immersion blender or a handheld electric mixer.
If using a jar, shake vigorously for 60 to 90 seconds until the mixture thickens and forms soft peaks. If using a mixer, blend on medium-high speed until the mixture holds its shape but is still pourable. Do not over-whip to the point of making stiff whipped cream.
Taste the foam and add a small amount more sweetener if needed.
Spoon the finished strawberry cold foam over your favorite iced coffee or cold brew.
Notes
For a thicker foam, use slightly less milk. For a thinner foam, add a splash more milk.
If you do not have an immersion blender, you can use a whisk, but this will require significantly more arm strength and time.
This recipe makes enough topping for 2 to 3 large iced drinks.
Use a high-quality strawberry syrup for the best flavor copycat result.