Pop six cups or glasses (about 200ml each) into the freezer to get super-cold, and chill the soda water and berries in the fridge.
In a jug, cover the gelatine with cold water and leave for just 5 minutes, while you hull any strawberries, halving or quartering any large ones.
Pick the mint leaves, slicing the bigger leaves, and arrange in the cups or glasses with the rest of the berries.
Briefly heat the cordial with 50ml of water in a small pan until it just starts to bubble, then turn the heat off.
Remove the gelatine leaves from the jug and whisk into the pan until melted, then chuck in the ice cubes to start to cool the mixture.
Pour in the cold soda water, then divide it all between the cups or glasses, gently pressing down to submerge the fruit.
Chill in the fridge for at least 6 hours, or until set, hopefully with bubbles suspended.
To serve, arrange 3 sponge fingers on each of your serving plates.
Zest over the oranges, then squeeze the juice over the sponge fingers, to soften.
Carefully dip each jelly mould into a bowl of boiling kettle water for long enough to loosen the jelly, then turn out on to the sponge fingers.
Top with yoghurt and scrape or grate over some chocolate, to finish.
