Makes 8 crostatas.
For the pastry, stir the flour and salt together in a mixing bowl. Add the butter and cut in using your fingertips or a pastry cutter. Whisk the sugar, egg and egg yolk together and add this all at once to the flour, stirring with a wooden spoon until the dough comes together. Shape this into 2 discs, wrap in plastic wrap and chill for at least 2 hours before rolling.
For the fruit, bring the apples, cranberries, raspberries, blueberries, sugar, vanilla and cinnamon up to a simmer over medium heat in a saucepan. Simmer the fruit, stirring occasionally until the apples are tender and the cranberries have “popped”, about 15 minutes. Set aside to cool to room temperature (or make ahead and chill).
Preheat the oven to 350ºF (180ºC) and line a baking tray with parchment paper.
Lightly knead the first disc dough on a lightly floured surface (this makes it easier to roll without cracking) and roll it into a square that is 1/4-inch (6 mm) thick and 10-inches (25 cm) across. Using a ruler or back of a knife to indent the dough without cutting through, mark a cross from top to bottom and across and then from opposite corners (like an asterisk) – this will give you 8 triangles. Spoon some of the chilled filling in the centre of each triangle.
Roll the second piece of dough to 12” (30 cm) square , 1/4-inch (6 mm) thick. Cut this into strips about an inch (25 mm) wide. To make a lattice that covers the base, lay half of the strips in one direction over the jam-covered based, leaving about an inch (25 mm) between them. To start the lattice, fold back alternating strips about 2 –inches (5 cm) back and lay one strip perpendicularly over the strips laying flat. Fold back the pastry strips so they rest over the newly laid one. Now fold back the opposite strips from the other side, and lay the next pastry strip next to the first perpendicular one and return the folded strips back. Repeat this alternating technique until you have a basket weave of pastry. Gently press around the fruit (along the triangle shapes made by the indentations made on the base dough) to secure the pastry in place. Trim around the edges of the square and then cut the pastry into their triangle portions. Transfer these to the prepared baking tray using a lifter.
Brush the turnovers with the eggwash and sprinkle them with the cinnamon sugar. Bake the turnovers for about 25 minutes, until a rich golden brown. Once cooled, dust with icing sugar and serve.