First, we make the dough. In a large bowl, work quickly to add the butter to the flour & toss. Use your fingers to press each cube of butter into a flat sheet, tossing the butter throughout to make sure each piece remains 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, for me this was 6 tablespoons. Split the dough into two disks & wrap each in cling film. Leave to rest in the fridge for at least 2 hours before using. Extra chilled dough = extra flaky pastry.
When the dough is ready, remove one of the disks from the fridge and roll out into a rectangle – roughly a 1/4-inch thick. Carefully fit this sheet into the pie tin & trim a 1-inch boarder around the edges. I re-rolled my scraps into another long rectangle, sliced it up, and braided it. I then re-rolled my scraps again and used a piping tip to cut out circles. Using a pastry brush, paint a thin layer of egg wash along the edges of the pie base – this will glue your braids/circles etc onto the base. When complete, place the tin into the fridge.
Preheat the oven to 250C.
Now we make the filling. Combine all of the ingredients in a medium bowl. Leave to stand for 5-minutes before using.
Meanwhile, make the crumble. In a large bowl, combine all of the ingredients. Use your fingers to break the butter down into the mixture until it resembles coarse breadcrumbs. Set aside.
Assemble the pie when the oven is pre-heated. Remove the base from the fridge, pour in the blueberry filling – juice and all. Cover the filling with a generous layer of crumble that’ll bring it to the lip of the dough, about half of what you made. Use a pastry brush to paint the edges of the dough with egg-wash & sprinkle with demerara sugar.
Place the pie tin onto a baking tray & bake for 35-40 minutes, until deep golden brown & bubbling. Allow to cool before slicing.