Mash or purée the raspberries and mix with the vinegar, pour into a jar and leave in the fridge for a day. Then pour the mixture into a fine sieve and press all the juice through, discarding the seeds, and return to the fridge. Cut the stone fruit into halves and remove the stones. Put the fruit and mixed berries in a bowl (non-aluminium), add the icing sugar, mix gently and store in the fridge for 6 hours. An hour before serving take the fruit from the fridge and gently mix in the raspberry vinegar.
For the shortbread, set the oven to 170°C/340°F/Gas 3—4. Cream the softened butter and caster sugar. Sieve the flours and add to the butter, mixing well, then add the ground almonds and work gently into a dough. If it seems a little sticky add a little more sifted flour. Either roll the dough into logs and rest for 30 minutes before cutting into slices, or rest the dough for 30 minutes before rolling out and cutting with a biscuit cutter. Place on a baking tray you have lightly buttered or covered with baking parchment and put into the preheated oven for 20 minutes. The biscuits should go a pale gold colour. Remove from the oven and cool on the tray for 2 minutes before transferring to a rack. When cold, store in an airtight container.
Serve the fruit salad with the shortbread and mascarpone.