In a large bowl, whisk together the spelt flour, buckwheat flour until mixed.

Using the large holes of a box grater, grate the frozen butter into the flour. Continue by cutting the butter into the flour with a fork or a pastry cutter until well incorporated and mixture resembles fine crumbs.

Cut in rendered fat.

Add all the water and mix until forms a dough.

Form into a ball, dust with flour, and flatten into a disk, wrap in plastic wrap or wax paper and refrigerate until firm, at least 30 minutes.

Preheat the oven to 350°F / 180°C.

Meanwhile, in a large bowl, toss the apples slices together with the brown sugar and cinnamon until fully coated.

For the pudding, in a small bowl, whisk together the eggs and milk. Add the sugar and vanilla pudding powder and continue mixing until fully combined and there are no lumps.

Remove dough from fridge, let rest for a couple of minutes.

Using 2/3 roll out of the dough, roll out on a floured surface in a thin layer large enough to line the bottom and sides of the pie dish.

Butter the pie dish and carefully arrange the thin crust in it (this is quite easy with floured fingertips).

Trim any excess dough and tuck the edges under if you want to create a thick edge. Crimp the edges of the crust with your fingers or use a fork to decorate.

Arrange the apple slices in the pie dish and carefully pour the pudding mixture over them so that it is evenly distributed.

Roll out the remainder of the dough and cut into thin strips and place as a grid over the apples. Alternatively, crumble it over the apples.

Bake for 45-50 minutes, until top crust is nicely browned and the apples are tender. Remove from oven and allow to cool before serving.