1. Add the prunes, port, orange juice and rind to a small saucepan with 1 cup of water. Bring to a simmer and cover with a round of baking paper. Simmer for 20 minutes, stirring occasionally, then strain to remove the prunes and rind, reserving the syrup. Roughly chop the prunes and set aside. Cut each sponge cake layer into 2 to form 4 layers.

2. Set one layer aside and cut the remaining 3 in half to create semi-circles. Line a large bowl or pudding basin with cling film, with plenty overhanging, and arrange the semi-circles around the bowl so they overlap like the petals of a flower, with the points meeting in the centre. Brush the sponge with the port and orange syrup, reserving some for the "lid".

3. Place the cream in a large bowl and whip to soft peaks with electric beaters. In another large bowl, combine the ricotta and mascarpone and beat until smooth (you don't need to wash the beaters in between). Fold the cream into the cheese mixture, then divide again back into two equal portions. Fold the prunes (and any orange rind mixed with them) into one portion of the mixture, reserving a little for garnish.

4. Beat the cocoa into the other, then fold through the chocolate and walnuts. Spread the chocolate mixture in an even layer inside the sponge "shell", then add the prune mixture to fill. Brush the reserved sponge layer "lid" with the remaining syrup and place on top. Place a plate on top and refrigerate for at least 4 hours to firm. Ease from the mould onto a serving plate, dust with icing sugar and cocoa, and scatter with the reserved chocolate, walnuts and prunes.

If you like this recipe, try Adam Liaw's Swedish baked salmon pudding.