Start by removing any worn or bad or bruised bits from the sweet potato, then cut into 5mm slices and put into a saucepan.
Add enough water to cover the potato slices and boil until soft enough to mash.
Remove the ends from the shallots and the very outer skin.
Remove the leaves from the mint then wash and chop finely.
Put the chopped mint into a watertight container and add the sugar and 3 tablespoonfuls of boiling water and the vinegar.
Add a tiny sprinkling of salt.
Stir and leave to rest for approximately 20/30 minutes.