Preheat oven to 180°C and line the base and sides of a 20cm square baking tin with baking paper.

In a food processor, combine the flour, salt and sugar. Add the chunks of butter and process until it forms large clumps - this may take a minute or so. Press the dough firmly and evenly into the tin. Bake for 15 minutes or until very pale golden.

In your food processor (don't bother washing it out), grind the pistachios, flour, salt, and sugar to a powder (or as fine as you can make it!). Add the butter and process until no longer visible. Add the egg and vanilla, blending until it forms a smooth paste.

Spread the filling evenly over the cooked base.

Toss the sliced fruit with the orange zest and juice, and evenly spread over the pistachio paste.

Bake the slice for 50 minutes, or until golden and a skewer inserted into the pistachio comes out clean. Leave in pan to cool.

Dust with icing sugar to decorate and cut into squares.

Keep left over slice in the fridge in an air-tight container.