In a large bowl, toss the sliced bananas, the chopped nectarines or peaches, whichever you are using, and the quartered strawberries with one tablespoon of the caster sugar and the lemon juice. Divide between individual bowls, adding a few blobs of the mascarpone or whipped cream, whichever you’re using, to each one.
Next, make the caramel to go on top. Place the 100g (3ƒoz) caster sugar in a small to medium saucepan on a medium heat and stir. It will begin to look lumpy and sandy, but don’t worry – just keep stirring. Eventually, it will become viscous, turning from golden to a rich caramel colour. Altogether, this can take up to about 12 minutes.
Using a spoon, carefully drizzle all the caramel over the mascarpone or whipped cream, whichever you’re using, and over the fruit. Set aside for about five minutes, just to allow the caramel to cool and set hard, then serve.