Boil the potato until it's soft enough to be easily pierced with a fork. Once it's cooked, drain, peel and mash it. Leave it to cool.
Combine flour, sugar, yeast, mixed spice, aniseed, and salt in a large bowl.
Add the mashed potato to the bowl and mix it into the dry ingredients.
Gradually add the lukewarm water and milk to the mixture, kneading the dough until it's smooth.
Cover the bowl with a damp cloth and let it rise in a warm area for about an hour or until the dough has doubled in size.
In the meantime, prepare the syrup by combining sugar, water and a cinnamon stick in a medium saucepan. Bring the mixture to a boil and stir until all the sugar is dissolved. Keep the syrup warm.
Once the dough has risen, knock it down and divide it into small equal portions. Roll each piece into a smooth ball.
Heat the oil in a deep fryer or a heavy-based saucepan and deep fry the balls of dough until they're golden brown. Ensure to turn them so that they cook evenly.
Using a slotted spoon, remove the koesisters from the oil and immediately dip them into the warm syrup. Allow the koesisters to soak for a few minutes, then remove them from the syrup and let them drain on a cooling rack.
Roll the syrup-soaked koesisters in desiccated coconut and serve while still warm.
