To make the filling, peel, core and chop the apples into 1cm (1/2 inch) cubes.
Combine the apples, sugar, cinnamon and water in a saucepan. Cook, over a low heat for 15 - 20 minutes, stirring occasionally. The apples should be soft but still hold their shape.
Drain the juice from the apples into a small bowl. Stir in the cornstarch until it dissolves and return this mixture to the apples. Mix to combine. Set aside to cool.
To make the pastry, preheat the oven to 180 C (350 F) and line a 9 x 13 inch pan with baking paper.
Sift the icing sugar into the bowl of your stand mixer. Add the flour and salt. Fit the mixer with the paddle attachment and mix on a low speed to combine. Add the butter and mix on a low speed just until a dough forms.
Put the dough in the pan and press it evenly into the base and up the sides. This will take a little time and is annoying, but keep at it.
Line the crust with parchment paper and fill with pie weights or dried beans. Bake the crust about 25 – 35 minutes, until it evenly colours to a golden brown. I had to uncover mine for the last 5 minutes.
Meanwhile, make the crumble. Mix the flour, almond meal, butter, sugar and salt together using an electric mixer fitted with a paddle attachment, on a low speed for 4-5 minutes, until a buttery crumble forms.
Once the crust is baked and golden, remove it from the oven and discard the baking paper and beans. Spread the apple filling evenly in the crust. Sprinkle the crumble evenly over the apples, clumping some bits together.
Bake for 25 - 30 minutes, until golden brown. Allow to cool before cutting. Makes 20 pie bars.
Recipe by Butter Baking at https://www.butterbaking.com/2012/09/17/apple-and-almond-crumble-pie-bars/