This is actually the "Black & White Tart" recipe from Nigella's book. But since we can't find the white berries and blackberries, kiwis will do just fine ^_^
1. In a food processor, blitz the biscuits until fine
2. Melt the butter and while the motor running, add in slowly to the crumbed biscuits.
3. Mix until well combined, then pressed onto fluted pie tray with removable base.
4. Place into the fridge while you make the filling. (I think it's probably best if you let in sit in the fridge for 1 hour at least, for the butter to solidify and set)
1. Beat the egg white until stiff peak just formed, set aside.
2. In another bowl, beat the egg yolk and sugar until thick and pale (as Nigella says, be patient at this stage. It looks like crumbs in the beginning and seems impossible to get it together. It took me a good 10-15minutes of continuous beating until it comes together and becomes thick and pale)
3. Add in the mascarpone, lemon/lime juice and rum. Mix well until smooth.
4. Fold in the egg white until combined.
5. Pour into the set biscuits base, then top with thinly sliced kiwi.
6. Return it to the fridge, and let set for about an hour.