In a large mixing bowl, whisk together the all-purpose flour, granulated sugar, and salt.

Add the cold, cubed unsalted butter to the flour mixture. Use a fork or pastry cutter to mix until the mixture resembles coarse crumbs.

Slowly add the cold water, mixing until the dough comes together. Avoid overworking the dough.

Divide the dough into two halves, shape them into discs, wrap in plastic wrap, and refrigerate for at least 1 hour.

Peel, core, and slice the apples into thin wedges.

In a large skillet, melt the unsalted butter over medium heat. Add the sliced apples and cook for about 5 minutes, stirring occasionally.

Sprinkle the brown sugar, ground cinnamon, cornstarch, and salt over the apples. Stir in the water, and cook for an additional 5-7 minutes until the apples are tender and the mixture thickens. Remove from heat and let cool.

Preheat your oven to 220°C (425°F).

Roll out one disc of dough on a floured surface to fit your pie dish, then transfer it to the dish. Trim any overhanging edges.

Sprinkle almond flour evenly over the bottom crust to absorb excess moisture.

Fill the crust with the apple mixture, spreading it evenly.

Roll out the second disc of dough and place it on top. Seal and flute the edges as desired. Cut slits in the top for steam to escape.

In a small bowl, whisk the egg with 1 tbsp of water and brush it over the top crust. Sprinkle brown sugar over the egg wash for additional sweetness and crunch.

Bake the pie in the preheated oven for 45-50 minutes, or until the crust is golden brown and the filling is bubbling.

Let the pie cool for at least 30 minutes before serving it warm with a scoop of vanilla ice cream on top.