For the pastry, pulse the flour, butter and sugar in a food processor until the mixture resembles breadcrumbs.
Mix together the beaten egg and water. With the motor still running, gradually add the egg and water mixture to the bowl of the food processor a little at a time, until the mixture comes together as a dough.
Roll out the pastry onto a lightly floured work surface to form a circle about 30cm/12in in diameter. Carefully line a 25cm/10in tart tin with the rolled pastry, then lightly prick the base with a fork.
Transfer the tart case to a baking tray and chill in the fridge for 30 minutes. Preheat the oven to 200C/400F/Gas 6.
When the pastry has chilled, line the tart case with greaseproof paper and fill it with baking beans. Bake in the oven for 20 minutes, then remove the paper and beans. Return the tart case to the oven for a further 4-5 minutes, or until the pastry is pale golden-brown. Remove the tart case from the oven and set aside. Reduce the oven temperature to 170C/325F/Gas 3.
For the filling, in a food processor, blend together the butter and sugar until pale and fluffy. Add the ground almonds, flour, salt, baking powder, eggs and vanilla extract and blend again until well combined.
Spread the raspberry jam over the base of the pastry case, then spoon over the almond filling mixture, starting at the edges of the tart and working towards the centre.
Arrange seven of the peach halves, cut-sides down, in a circle at the edge of the tart, pressing each gently into the filling mixture. Press the remaining peach half into the centre of the tart. Push the raspberries into the filling mixture.
Bake the tart in the oven for 25-30 minutes, or until the filling mixture has set slightly and is pale golden-brown.
Remove the tart from the oven, sprinkle all over with the flaked almonds, then return to the oven and continue to bake for a further 20-25 minutes, or until the peaches are tender and the filling has risen and is golden-brown. Set aside for 15 minutes to cool slightly, then lift the tart from the tin.
Serve warm or cold in wedges with cream.