Put the vinegar in a saucepan with the ginger, brown sugar, mace and peppercorns. Bring to the boil, lower the heat and simmer for 3 minutes. Drain the onions and add to this mixture, continuing to simmer for 4 minutes.
Remove the onions to sterilized jars with a slotted spoon, then sieve in pickle to cover. Put on lids, allow to cool, then refrigerate for a week before eating.
© 1998 Alastair Little and Richard Whittington estate. All rights reserved.