For the crust: Combine flour and sugar. Rub in the butter until the mixture is crumbly. Add 2 tbsp cold water to form the dough. Do not knead. Wrap in plastic wrap and chill for 30 minutes.
For the crunchy base: Combine pistachios, sugar and cornstarch. Reserve.
For the filling: In a bowl, mix all the fruit with the lemon juice, cornstarch and sugar. Reserve.
To assemble: Preheat oven at 180°C/350°F. Roll out the dough into a circle of about 30cm (11 inches) and place it on a baking sheet lined with parchment paper. Cover the bottom with the pistachio mixture leaving a 2-inch border. Pour in the fruit mixture, fold up the edges of the dough around the filling, and gently pleat to seal, pressing it with your hands. Brush the edges with a slightly beaten egg and sprinkle with light brown sugar. Bake for 45-55 minutes, or until the fruit is tender, the juice bubbly and the edges are golden. Optional: sprinkle pistachios over the top. Let it cool and serve with whipped cream, ice cream or just on its own.
