In a small pot, bring the water, sweet potato, cinnamon stick and aniseed to a boil. Simmer until the potatoes are tender, about 15 minutes. Set 1/2 cup (125 ml) of the cooking liquid aside. Drain the potatoes and return to the pot. Discard the cinnamon stick. Mash the potatoes with a potato masher until smooth, then transfer to a bowl and let cool for 5 minutes.