PIE DOUGH

1. Combine the ice, water, and cider vinegar in a bowl and stir lightly to combine. Place cups flour, salt, and sugar in a large bowl and stir lightly to combine. 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. 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 a rectangle and wrap tightly in plastic wrap. 
3. Repeat the process again. Place both rectangles of dough in the fridge to rest for at least two hours, or preferably overnight.

BROWN BUTTER OAT STREUSEL

1. Place the butter in a small pan, and place on the stove over medium heat. Heat, stirring occasionally, until the butter has melted. Continue to cook, until the butter begins to foam, smells nutty, and goes a deep golden brown colour. Remove from the heat and place in a medium heatproof bowl. Add the remaining ingredients, and mix well to combine. Using your hands, break up any large lumps.

ASSEMBLY

1. Have a quarter sheet pan (9" x 13" baking sheet) ready.
2. On a lightly floured surface, roll one of the rectangles of dough into a shape slightly larger than your sheet pan. You want it to be approximately ⅛ inch (3mm) in thickness. Line the pan, leaving the extra dough overhanging. Trim the dough so there is about 1 inch overlapping the edge of your dish. Fold the overlapping edge under itself, pressing down with your fingers to seal. This creates a border which helps prevent the edges of the pie from shrinking. Place in the fridge while you prepare the filling and lattice. Wrap any offcuts of dough in plastic wrap and place in the fridge until needed.
3. Roll out the second piece of dough, and cut lattice strips - we did an angled lattice and a braided edge. Place cut out lattice pieces on a baking sheet lined with parchment paper and refrigerate until needed.
4. In a large bowl, combine the cherries, sugar, tapioca starch, and salt. Transfer to the pastry lined sheet pan. Top with lattice strips. Trim back any overhanging pastry, and either crimp the edge or add a braided border, fixing down with a little egg wash.
5. Transfer the pie to the fridge for at least 30 minutes.
6. While the pie is resting in the fridge,  preheat the oven to 425˚f/ 220˚c. Place a baking tray on the bottom rack of the oven. Brush the pie with eggwash and sprinkle generously with extra raw sugar. Place on the baking tray and bake for 20 minutes, or until the pastry has set and is beginning to go golden. Remove from the oven, and add the prepared streusel around the edge of the pie. Reduce the temperature 375˚f / 190˚c, return the pie to the oven, and bake until the pastry is deeply golden and the filling is bubbling, 45 to 50 minutes.
7. Remove from the oven and allow to cool. Serve warm or at room temperature.