Preheat oven to 350-degrees F. Set aside a 12" oven-safe skillet (I like using cast iron) or a large baking dish.
Peel and evenly slice the apples (¼"-⅓" inch slices). Place sliced apples in a large mixing bowl.
To the bowl with the apples, add the cinnamon, nutmeg, arrowroot starch, coconut sugar and vanilla. Mix until apples are evenly coated. Transfer apples to baking skillet or baking dish.
1 ½ tsp. ground cinnamon, ¼ tsp. ground nutmeg, 2 tbsp. arrowroot starch, ¼ cup coconut sugar, 1 tsp. pure vanilla extract
In a separate, medium-sized bowl, combine the oats, oat flour, walnuts, coconut sugar, cinnamon and salt. Next, add the coconut oil (or butter) in roughly 1 tsp. sized pieces. Using a pastry cutter, cut the coconut oil into the oats until you have a slight coarse/crumbly mixture (the oil should remain in little clumps). Alternatively, you can use the back of a fork to cut the oil into the mixture, or just gently combine with your hands. Pour mixture evenly over the apples in the baking dish. Gently pat down to even out the mixture.
1 cup rolled oats/old-fashioned oats, ½ cup oat flour, ½ cup chopped walnuts, ½ cup coconut sugar, 1 tsp. ground cinnamon, ¼ tsp. fine sea salt, ¼ cup coconut oil, cooled in the fridge *see notes*
Bake uncovered for 45 minutes to 1 hour. Edges will be nice and bubbly and topping golden brown when done.
Allow to cool slightly. Best if served warm. Enjoy!