Boil blackcurrants, blackberries, sugar, 50ml water, and cassis in a pan.
Simmer for 2 minutes and strain through a muslin-lined sieve, reserving juice and fruit separately.
Dissolve 3 gelatine leaves into the heated strained juice and leave to cool.
Boil mixed berries with 50ml water for 3 minutes while mashing, then stir in 2 tablespoons cassis.
Blend the mixture into a fine purée and strain through a fine sieve into a pan.
Dissolve 4 gelatine leaves into the purée, then cool and chill in the fridge.
Boil 150g sugar and 50ml water until the syrup reaches 118°C.
Whisk egg whites to soft peaks and slowly pour in the hot syrup while whisking.
Whisk the double cream in a separate bowl until soft peaks form.
Fold the fruit purée and the whipped cream into the egg white mixture.
Cut the sponge to fit the chefs' ring and slice horizontally to create a thin disc.
Place sponge in the ring, drizzle with cassis, pour in mousse, and chill for 1 hour.
Pour the cooled jelly juice over the set mousse and chill for 2 hours until firm.
Decorate with figs, raspberries, and mint, then remove the ring using heat to loosen.