Add the water to a 5-quart pot, and bring to a boil. Once the water is boiling, add the tapioca pearls and boil for 20 minutes. They will float to the top fairly early in the cooking process; when this happens give them a stir.
After boiling for 20 minutes, reserve 2 cups of the cooking liquid, and then rinse and drain the boba.
Put the boba back into the pot. Stir in the reserved 2 cups of cooking liquid and the brown sugar. Cover the pot and let the boba steep for 20 minutes. Drain the boba except for 2 tablespoons of the liquid (this small amount of liquid will help prevent the pearls from sticking together).
For the Matcha Milk Tea:
While the boba is steeping, make the tea.
Add the lukewarm water and matcha powder to a glass jar with a lid and give it a good shake until foamy. Alternatively, add them to a bowl and whisk until it’s frothy.
To Assemble the Bubble Milk Tea:
To each of 4 glasses, add the following in this order: 2 tablespoons simple syrup, ½ cup prepared boba, ¾ cup ice, ½ cup coconut milk, and then divide the matcha tea between the 4 glasses (each glass gets about 2 tablespoons + 2 teaspoons of matcha tea).
Serve immediately.
Notes
How Much Boba This Makes: 1 ⅔ cups of dry black tapioca pearls cooks up to be about 2 cups of prepared boba. About ½ cup of prepared boba is a good amount for each drink, so you will get 4 drinks from 1 ⅔ cups of dry tapioca pearls.
Simple Syrup: To make about ¼ cup of simple syrup, combine ¼ cup granulated sugar and ¼ cup filtered water in a small saucepan over medium heat. Bring to a boil, and then boil for 30 seconds. Remove from the heat and cool to room temperature before using. Feel free to add more or less to taste.
Best Served Immediately: Cooked tapioca pearls continue to absorb liquid. This causes them to expand more and take on a gummy texture. Additionally, you may have trouble getting them through a straw (even a large bubble tea straw) if this drink sits for quite a while.
Can I Prepare Boba in Advance? For the best flavor and texture, I recommend eating boba immediately after making it. However, if you prepare extra tapioca pearls, you can store them in simple syrup in the fridge for up to 2 days.
Coconut Milk: Use full-fat canned coconut milk for an even richer beverage.
Vanilla: Add about ½ teaspoon vanilla extract per drink for a mild vanilla flavor that complements green tea well.