We make our Yorkshire pudding the equal amount way , get 3 glass tumblers the same size ( I don't fill to top as don't need to feed that many ) so in one put eggs , in another up to same level with plain flour , pinch of salt , and the other glass equal level milk but then the big difference was dh poured the small amount of double cream we had left over to the milk.
Carried on as usual , put in oven at 15 minutes later this has rose up ! Never had it so high so can only be addition of cream.