Soak the gelatine leaves in cold water until softened, about 5 minutes.
Heat the cordial with the sugar over a low heat until all the sugar has dissolved.
Strain the gelatine and gently squeeze out any excess water then add to the sugar mixture.
Bring to a simmer and cook for 3 minutes, until the gelatine has melted.
Remove from the heat and leave to cool a little, then pour in the sparkling wine and stir.
Divide half the raspberries into 6 or 8 glasses, or any other container that holds at least 180ml.
Pour the liquid to fill one third of the container and chill for 2 hours.
Add the remaining raspberries and top up with the rest of the liquid.
Chill for 4 hours or overnight, until set.
Serve with fresh mint garnish.