Frangipane is traditionally made with almonds but it's also delicious with roasted unsalted cashews. You can make the frangipane the day before and store it in the freezer in a container with a tight fitting lid so it won't dry out.
Process cashews in your food processor till fine. Add icing sugar and continue to process till it forms a paste. If the mixture is dry, add a couple of teaspoons warm water and process till smooth. Set to one side.
Make the shortcrust
Add all ingredients to your food processor and process till the mixture forms a ball.
Grease an 20x20cm (8 inch) square baking tin and line with greaseproof paper. Roll out the shortcrust pastry to cover the bottom of the tin.
Place the tin in the freezer for a few minutes to firm up the pastry.
Make the filling
Knead the frangipane with the egg and the flour, either by hand or using the kneading attachent of your electric mixer. Set to one side.
Bring a saucepan with water to the boil. Make an x shaped cut at the bottom of each peach and blanch the peaches in the boiling water for about 1 minute. Remove from the boiling water and dip into cold water, then remove the skin.
Cut peaches in half and remove stones, then slice peaches.
Preheat your oven to 180 C / Gas 4.
Evenly spread the frangipane over the shortcrust using a spatula. Be careful not to disturb the shortcrust layer.
Arrange the peaches on the frangipane layer in a slightly overlapping pattern.
Bake in the preheated oven till the pastry is golden brown and the filling is set, about 45 to 50 minutes.
Gently transfer the tart with the greaseproof paper to a wire rack till cooled (if you leave it in the baking tin, it will not harden but will get soft). You can return the tart again to the baking tin after it has cooled.