Turn off the heat and immediately add the flour, constantly stirring. The resultant dough should be lump-free and semi-solid. If there appears to be lots of lumps then break them up using a large fork. If the dough has become too solid then add more warm water. If it seems to be very runny, wait for a few minutes before adding any more flour, as sometimes the extra water is absorbed by the flour and you will still get semi-solid dough.