Soak the gelatine in some cold water for 5 minutes to soften.
Put 50ml of water (use less fresh water if you are using some of the oyster brine) and the sugar in a small saucepan. Bring to the boil and simmer until the sugar has dissolved.
Squeeze out the excess water from the gelatine and add to the pan stirring until it dissolves.
Remove from the heat, add the sherry to the mix, combine well and then pour into a small deep container.
Cool and then refrigerate for at least 3 hours or until set.
Heat a little oil in a frying pan and add the pancetta.
Cook until crisp and drain on paper towels.
Crumble into pieces.
When ready to serve, shuck the Mahurangi oysters and put them onto a bed of ice.
Cut the jelly into small cubes, put a few on each oyster.
Scatter with the pancetta and the chives.
Serve with more chilled manzanilla.