Put the fruit into a saucepan, add the sugar, then cook gently until the sugar has dissolved and the liquid is slightly syrupy. Remove half of the berries and juice to a bowl, stir in a tablespoon of cassis, then set aside to cool.
Add the apple juice to the fruit in the pan, and bring to a simmer. Taste the fruit, and add a little more sugar if necessary. Remove from the heat, and add the remaining cassis.
Soak the gelatine leaves in a bowl of cold water for five minutes, until soft and floppy. Lift the gelatin from the water and squeeze out the excess liquid.
Add the gelatine to the fruit in the pan and stir until it has completely dissolved. Remove from the heat, and transfer the jelly mix to a bowl. Allow to cool, then chill in the fridge until the mix has set to a softly wobbling jelly.
Cut the madeira cake into 1cm/½in slices. Give the fruity jelly a stir - it should be softly set. Layer the cake, jelly, fruit and juice in the bottom of a trifle dish (roughly 20cm/8in diameter).
For the custard layer, put the mascarpone into a large bowl then add the custard. Whisk together until creamy and smooth. Spoon the custard over the fruit and sponge.
Whip the cream until soft peaks form when you remove the whisk from the mixture.
Spoon the cream over the top of the trifle, starting from the outside and working in. This will avoid the cream sinking into the custard.