Put the water and sugar into a small saucepan over a low to medium heat. Stir to dissolve the crystals, then raise the heat and bring to a boil. Reduce the heat, simmer for five minutes, then remove the pan.
Pour the sparkling wine into a large heatproof bowl and add the gelatine. Set aside for about five minutes, or until the leaves are soft and squidgy.
Take out the leaves, squeeze off as much liquid as possible, and add them to the sugar syrup.
Whisk furiously until the gelatine has completely dissolved, then pour the syrup back into the bowl with the sparkling wine and whisk to combine.
Allow to cool thoroughly, then refrigerate the jelly for about one hour.
As soon as it starts to thicken, stir in the raspberries or other fruit.
Divide the jelly between six glasses and cover them with cling film.
Refrigerate for four to six hours, or until they have completely set and serve.