For the pastry: Mix the flour, salt and caster sugar together into a bowl. Add the diced butter, rubbing in with your hands until it resembles breadcrumbs. Add the water 1tbsp at a time until the dough starts to come together. Turn out onto a lightly floured worktop, and knead until it comes together to form a uniform dough. Wrap the dough in clingfilm and put in the fridge for 45 minutes.
Once chilled, roll the pastry out on a floured work surface into a rectangle about 2-3mm thick. Line the tin with the pastry and then pop back in the fridge for 30 minutes or until firm. Then, pre-heat the oven to 180C/160C fan/Gas Mark 4.
For the frangipane: While the pastry is chilling, place the butter in a large bowl, and beat in the sugar. Then beat in the ground almonds, egg and almond extract. Set aside until needed.
Once the pastry is firm, line it with baking paper and baking beans, then bake for 20 minutes. Then remove the beans and baking paper and bake for another 5 minutes until the pastry is dry. Remove from the oven and leave to cool for 5 minutes.
Spread the raspberry jam evenly in the pastry case, top with the frangipane - again spreading evenly. Finally, sprinkle the flaked almonds over the entire tart then return to the oven for 25-30 minutes until golden.
Once baked, remove the tart from the oven and leave to cool completely in the tin. Before serving, dust with icing sugar for a pretty effect!