To heat food at the lowest possible temperature. Below 'simmering' probably only possible by the use of gas appliances. The word FURKLE was invented by Paul Kelly (English) and mentioned first in letters home (2000) and also in his blog 'Daze Off' (whilst teaching Americans how to cook Curry).
KEITH FLOYD (The chef) once stated that he didn't think there was such a word (to describe the lowest possible gas setting whilst cooking food slowly).
To 'furkle'. Cooking on a domestic gas cooker, food would be first cooked and browned and once all ingrediants had been cooked through, the gas would be set as low as absolutley possible, so low as to just 'furkle' the food, to keep the heat sufficient to maintain a low heat, slight bubbling and nominal steam.