Steep your black tea in boiling water for 5-10 minutes. Remove the tea bags or tea leaves and set aside to chill in the fridge.
Peel and chop a small sweet potato into medium chunks. Add them to a pot with enough water to cover the sweet potatoes. Cover and bring to a boil on high heat. Remove the lid and let it boil uncovered for about 15 minutes or until the sweet potatoes become soft and easily pricked with a fork.
Drain the water and use a fork to mash the sweet potatoes into a paste. Weigh out 100g of this mashed sweet potato to a small bowl.
Add glutinous rice flour and tapioca starch to the mashed sweet potato. Stir together with a spoon and then knead together with your hand until it forms a soft dough that isn't too sticky. Add a bit more tapioca starch if the dough is too wet, as needed.
In a separate small bowl, sprinkle in a bit of tapioca starch and dust your hands with it. Pinch off small bits of dough and roll into small balls with your fingers. Add the rolled pearls into the new bowl and swirl it around occasionally to coat the pearls with tapioca starch to prevent them from sticking together. Repeat with all remaining dough.
Bring a small pot of about 2” of water to a boil. Drop in your rolled pearls and immediately give them a stir.
Cook pearls for about 5 minutes until they float to the surface and are cooked through.
Drain the water from the pot and transfer the cooked pearls to a small bowl with brown sugar and a few tablespoons of cold water (or ice cubes) to keep the pearls from sticking together. Give it a stir and let the pearls soak in the brown sugar syrup while you prepare the rest of the drink.
In a small jar with a tight lid (mason jar works well), add the whipping cream, granulated sugar, and cinnamon. Screw on the lid and shake vigorously for about 1 minute until the cream thickens but is still pourable.
In each serving glass, add about 100g of sweet potato boba pearls. Fill the rest of the glass about ¾ full with ice. Pour in about 150g of black tea and top with about 70g of sweet cream. Stir together before sipping with a boba straw!