In a small mixing bowl, add the whole milk, heavy cream, sea salt, and sugar.
Using a hand mixer, cold foam frother, or blender, start mixing on a low speed. Gradually increase the speed to create more foam. Move in an up and down motion first, then circular. Keep mixing until the milk has thickened and formed a foam. This usually takes around 2-3 minutes.
Once the milk foam forms with a medium peak, it is ready. Spoon it on top of your bubble tea drink.