Cook fruit and sugar in a saucepan until dissolved and syrupy.
Reserve half the berries with a tablespoon of liqueur to cool.
Simmer remaining fruit with apple juice and adjust sweetness with sugar.
Stir in remaining liqueur and remove from heat.
Soak gelatine in cold water for five minutes then squeeze dry.
Dissolve gelatine into the warm fruit mixture.
Chill the jelly mixture until it is softly set.
Layer 1cm cake slices, jelly, and reserved fruit in a 20cm dish.
Whisk mascarpone and custard together until smooth and spoon over layers.
Whip cream to soft peaks and spread over the custard.
Chill for one hour and garnish with toasted nuts before serving.