Break the egg in a bowl and stir to mix. Divide the mixture in two equal parts. Or if you opt to use a flaxseed egg here, combine flaxseed meal and water (don't divide in 2; everything is used in the dough).
Add flour, baking powder, 2 tsp of cinnamon and salt to a medium mixing bowl and stir well to combine.
Add ½ of the egg (or all flax egg), margarine, coconut sugar, vanilla extract and knead well to form a dough. Divide into 3 equal parts.
Preheat the oven to 350F/175C.
In the meantime cut apples in cubes. Mix coconut sugar and cinnamon together in a cup and add to the apples. Toss to coat.
Grease the springform with margarine or coconut oil. Use 1/3 of the dough to cover the bottom of the form and the other 1/3 for the side. Using your fingers, spread and press the dough down. Sprinkle the bottom with oat flour (this is to absorb the moisture from the apples).
Roll out the leftover ⅓ of the dough and, with a knife, cut out strips (2cm/ 3/4 inch width) for a lattice.Add the apple mixture to the pie crust in the springform. Now add strips of dough on top to make a lattice (see photos). Apply remaining egg mixture (egg wash) to the lattice. If you are using a flaxseed egg skip this part. Bake the pie for 60 minutes until golden brown.
Take the pie out of the oven and let cool off a bit. Serve a warm slice with whipped (coconut) cream or a scoop of (vegan) ice cream. Store leftover pie covered in the refrigerator.