Pour about 550 ml of milk into a saucepan, add sugar and put it on the fire to warm up. Add pudding or cocoa with starch to the remaining milk, stir well with a whisk so that there are no lumps. When the milk is well heated, almost boils, pour in a thin stream of diluted pudding and, stirring all the time, cook until thickened, about one to two minutes. Remove from the heat and continue stirring for three minutes, add a piece of butter and mix everything until the butter dissolves. Cover the cream with cling film and set aside.