Mix soy milk and black sesame paste. This can be done in a mug with a frother or simply by stirring vigorously. If black sesame paste is not dissolving easily, warm up your milk on stovetop or in the microwave and the paste should easily mix.
Pour black sesame milk into a 12oz glass filled to the rim with ice while you prepare your matcha. (if you have warmed your milk, let it cool before pouring over ice).
Sift teaspoon of matcha powder into a bowl and add the hot (but not boiling) water. Whisk with a bamboo whisk or mix with a frother until matcha is dispersed.
Pour matcha into your prepared glass with black sesame milk. If wanting to create a layered effect, aim the stream of matcha to hit the ice cubes rather than directly into the milk. Serve immediately.
I have become an Asian grandma who likes things bitter and unsweetened, so I do not add any sweetener. I find with a really high quality matcha, the natural sweetness from the milk is enough for me. However, if you have a sweet tooth, feel free to add a sweetener of choice to the milk when you mix it with the black sesame paste.