Preheat the oven to 200?C/fan oven 180?C /gas mark 6. Line a large baking sheet with baking parchment. Make the pastry by placing the flour into a food processor with the cubed and chilled butter. Whizz until it resembles breadcrumbs. Add the soured cream and whizz until it just comes together. Turn onto a floured surface and gently knead until a dough is formed. Wrap the dough in clingfilm and chill in the fridge for one hour. For the filling, place the butter and sugar in a medium mixing bowl and beat them together with a wooden spoon until they are light and fluffy. Gradually beat in the eggs and then stir in the ground almonds. Add the almond extract, cover and set aside. Roll the pastry out onto a lightly floured surface to a 30cm/12in circle, then transfer it to the lined baking sheet and prick all over with a fork. Spread the almond mixture over the centre of the pastry leaving a border of about 4cm/1½in around the edge. Arrange the peaches around and on top of the frangipane. Then fold about 2½cm/1in of the pastry into the centre, over the fruit. Chill in the fridge for 20 minutes. Bake for 30-40 minutes until golden brown. If it is browning a bit too much towards the end of the cooking time, cover the tart with foil. Leave the tart on the baking sheet for ten minutes before carefully sliding it onto a serving dish. Place the apricot jam in a small pan and gently warm it over a low heat. Brush the melted jam or jelly all over the top of the tart, including the pastry. This tart is equally delicious served hot, warm or cold but must be devoured with lashings of cream or ice cream!