In a saucepan, heat the lemon zest in 20 cl milk over low heat and then add the sugar. Heat until the milk turns yellow.
Leave to cool and add this mixture to the remaining milk, including the zest. Bottle and refrigerate for at least 2 hrs.
Filter the milk, mix with the Yogurt and lemon flavour until smooth and then pour carefully into the pots.
Cook for 8 hrs in Yogurt mode.
Leave to cool and then refrigerate.