For the passion fruit cream, bring the double cream and 150g/5oz of the sugar gently to the boil in a large saucepan, then remove from the heat. Whisk in the lime juice and half of the sieved passion fruit pulp.
Pour the cream mixture into four large Martini glasses (do not fill to the top) and chill in the fridge for at least two hours, or until set.
Meanwhile, drain the gelatine leaves and shake dry. Bring 100ml/3½fl oz of water and the remaining sugar to the boil in a large saucepan. Add the gelatine leaves and whisk until completely dissolved.
Add the remaining sieved passion fruit pulp to the sugar syrup mixture, then set aside to cool.
When the gelatine mixture has cooled and the cream has set, pour one-quarter of the gelatine mixture on top of each portion of set cream to form a thin layer about 0.5cm/¼in thick. Return to the fridge for another hour, or until set.
Meanwhile, for the biscotti, preheat the oven to 180C/350F/Gas 4. Line a baking tray with baking parchment.
Place all of the biscotti ingredients into a large bowl and stir until the mixture comes together as a soft, sticky dough.
Divide the dough in half and roll each portion out into a sausage shape on a lightly floured work surface.
Place the pieces of dough onto the prepared baking tray and bake for 20-30 minutes, or until golden-brown. Remove from the oven and set aside for 10 minutes to cool and firm up.
Using a serrated knife, slice 1cm/½in-thick discs from the pieces of dough, slicing them at an angle. Lay the discs onto the same baking tray (use an extra baking tray if necessary). Return the biscotti to the oven and cook for 6-8 minutes, then turn the slices over and cook for a further 10-15 minutes, or until crisp and pale golden-brown on both sides. Remove from the oven and transfer to wire racks to cool.
Serve the passion fruit creams with the biscotti alongside.