Preheat the oven to 250C.
First, make the pie dough. In a large bowl, working quickly to add the butter to the flour & toss around. Use your fingers to press each cube of butter into a flat sheet, tossing the butter throughout to make sure each piece is covered. If at any time the butter seems warm, refrigerate the bowl briefly. Sprinkle about 4 tablespoons of ice water into the bowl & use a gentle hand to stir together until just combined. You’ve added enough water to the mixture if you can pick up a handful of the dough & easily squeeze it together without it falling apart, but without it being all sticky. Split the dough into two disks, each wrapped in cling film & leave to rest in the fridge for at least 2 hours before using. Extra chilled dough = extra flaky pastry.
Once the dough has chilled, remove one of the disks from the fridge. On a lightly floured surface, roll it out into a roughly 12-inch circle that is about ¼-inch thick. Carefully press the dough into your skillet / pie dish & crimp the edges however you like. Cover the entire dough with a sheet of tin foil, fill the foil with baking beans, and bake in the preheated oven for 20 minutes, or until the sides are slightly puffed & lightly golden brown. When ready, remove from the oven & gently lift off the tin foil. Leave to cool slightly.
Meanwhile, make the crumble topping. Using your fingertips, combine all of the ingredients in a large bowl until crumbs start to form – making sure to keep some of the bigger clumps in tact for extra buttery bits. Keep in the fridge until ready to use.
Now, the filling. In a large bowl, gently stir together all of the ingredients with a wooden spoon, ensuring that everything is coated evenly.
Fill the par-baked dough with the filling & cover with the prepared crumble. Bake for 30-minutes, or until the juices are bubbling & the crumble is a deep golden brown. Leave to cool slightly & serve warm with whipped cream.