Add all ingredients to a saucepan and cook until the apple is soft and thicken. set it aside to let it cool down.
To make the pie crust:
Preheat the oven at 175°C / 350°F.
Combine all ingredients in a bowl. They should stick together and like a pastry dough.
Press the crust mixture into the pie pan and bake at 175°C for 15 minutes. Let it sit on a wire rack to cool down. Keep the oven ON.
To make the apple pie filling:
While the crust is in the oven, make the apple pie filling: Place all ingredients in a saucepan and cook for 3 - 4 minutes until the apple is soft. Set it aside to cool down a bit.
To make the maple glaze:
Add all ingredients to a saucepan. Stir to combine and bring the mixture to boil. Once it boils, turn down the heat and cook to the ideal consistency.
Assembly:
Spread some maple glaze onto the crust, then layer the apple slices from outside inwards. Drizzle the left maple glaze on top. Sprinkle the chopped walnuts on top.
Return the pie pan to oven and bake for another 15 minutes until the crust is golden brown and your kitchen smells amazing!
Once finishing baking, let it sit for 10 minutes before removing from the pan. EAT!
*Oat flour: I often make my own by using my grinder to ground the rolled oats. You can use store-bought ones. If you are sensitive to gluten, make sure you choose the ones marked "gluten-free", like this gluten-free oat flour.
Storage: Store the leftover in an air-tight container in the fridge for 1 week or 2 weeks in the freezer.