Peel the rhubarb to remove the strings. Cut into pieces and put in a saucepan over medium heat. Add the grenadine syrup and stew for 10 min over low heat, stirring regularly until the syrup is fully absorbed. Leave to cool and spread on the bottom of the pots.
Mix the milk and Yogurt with a fork until smooth and pour carefully into the pots.
Cook for 8 hrs in Yogurt mode.
Leave to cool and then refrigerate.