It's best to make the onion mix the night before so that it is cold. Put the onion in a frying pan with a little oil & fry gently for a few minutes. Then sprinkle the brown sugar over the onion along with the salt & pepper and fry for another minute or two whilst stirring. Turn up the heat a bit & add the wine, keep stirring until the wine has just about evaporated, cool & chill overnight.