Add Thai tea mix to a steeping sock or coffee filter and place it over a heat-safe container or pot. Pour boiling water into the tea sock over the tea leaves. Let it sit for about 10 minutes.
Remove the steeping sock from the tea, squeeze out the remaining tea, and discard the tea leaves.
Stir in the condensed milk one spoon at a time while the tea is still warm, to taste. You want it to taste slightly sweeter than how you want it as it will be diluted after adding ice. Chill the tea in the fridge while you make the pearls.
In a medium pot, bring a full pot of water to a boil. Once boiling, add all the tapioca pearls and stir immediately to break up any clumps. Boil uncovered for 15 minutes.
Cover the pot, remove it from the heat, and let it sit for another 15 minutes.
Drain the water from the cooked pearls and transfer them to a small bowl. Add the brown sugar and stir together until the sugar has dissolved into a syrup.
To each serving glass, add 100g of pearls. Fill the glass half full or more with ice. Pour in your chilled thai tea until almost full. Top with a layer of heavy cream or half and half. Stir drink to mix before enjoying!