Lightly oil the bottom of a springform pan (26 cm Ø). Melt the butter. Finely chop the biscuits and mix well with the liquid butter. Use a tablespoon to press the biscuit mixture into the mould as a base.
Cover and chill for about 1 hour.
Soak gelatine in cold water. Wash and dry the limes and grate the peel of 1 lime finely. Squeeze both fruits. Mix mascarpone, sugar, lime juice, up to 1 tbsp. and peel.
Stir in yoghurt.
Squeeze out the gelatine and dissolve carefully at low heat. Stir in 3 tablespoons of cream, then stir into the remaining cream. Whip cream until stiff and fold in. Fill the cream into the mould and chill for about 15 minutes.
In the meantime, select the blackberries, wash and drain them if necessary. Wash, halve, stone and cut the nectarines into pieces. Mix with 1 tablespoon lime juice, drain on kitchen paper.
As soon as the cream begins to gel, cover the cake with the prepared fruit. Leave to cool for at least 3 hours.