PIE DOUGH

1. Make the pie dough in two batches - use half the dry ingredients and butter for each batch (2 ½ cups flour, pinch of salt, 2 tsp sugar, and 2 sticks butter), and use the apple cider vinegar ice water for both batches. Place flour, sugar and salt into a large bowl. Cut butter into chunks, and add to the flour. Toss lightly to coat. Working quickly, using a pastry blender or  your fingers,  cut the butter into the flour mixture until there are only pea-sized chunks left. You want a few lumps of butter remaining to keep the pastry nice and tender.
2. Combine ice, water and cider vinegar in a bowl. Sprinkle a few tablespoons of the ice water into the flour and butter mixture, and using a stiff spatula or your hands, mix in well. Continue adding water a tablespoon at a time ( I normally need about 8-10 tbsp) until you have a dough that holds together well, but is not too wet. Squeeze together with your fingertips to make a homogenous dough. Shape into two rectangles and wrap in plastic wrap. Repeat the process for the second batch. Rest in the fridge for at least two hours, or preferably overnight.

FILLING AND ASSEMBLY

1. Work with one batch of filling at a time - make all of the hand pies of that flavour, then rest in the fridge while you prepare the next batch of flavour. This reduces the chance of the filling releasing moisture in the bowl, meaning you leave some of the delicious juice behind.
2. In a medium bowl, toss the cherries and blueberries with the sugar and tapioca starch. Remove two of the rectangles of the dough from the fridge. Roll one rectangle out to ¼ inch (6mm) thickness. Using a ruler and pastry wheel or sharp knife, cut out 7 rectangles that are 9cm x 11cm (3 ½ x 4 ½ inches). Re-roll scraps if necessary to make enough rectangles. Place cut rectangles on a baking sheet lined with parchment paper and rest in the fridge while you roll out the second disc.
3. Roll out the second rectangle of dough - this is used for the tops of the pies. If you are keeping them plain 'pockets', cut out 7 more rectangles. Otherwise, cut a series of strips in a range of thicknesses to be used for lattices - you can decorate these however you like! I went with a range of lattices, braids, plain tops, and a few cut-outs using pie stamps. 
4. Working with one pie at a time, place 2 Tbsp filling in the centre of a rectangle. Top with your desired lattice or plain top, pressing down with your fingers to seal, then again using the tines of a fork to seal the lattice to the bottom of the pie. Place the hand pies in the fridge. 
5. Repeat the process with the blueberry and rhubarb filling, and the second two rectangles of dough. Rest in the fridge. 
6. While the pies are resting, preheat the oven to 425˚f / 220˚c. Remove the pies from the fridge, brush with egg wash, and sprinkle with raw sugar. 
7. Bake the pies for 30-40 minutes, checking after about 20 minutes, until they are golden brown and the filling is bubbling. Remove from the oven and allow to cool on the tray or on a wire rack. Serve slightly warm, or at room temperature.