Combine the oat flour, brown sugar, baking powder, cinnamon, pumpkin pie spice and salt in a large mixing bowl and whisk them together to aerate them. Combine the milk, apple sauce, apple cider, vanilla and egg yolks together in another bowl and whisk them together until it is smooth. Pour the wet ingredients into the dry ingredients and whisk them together thoroughly until it is a uniform batter. Take the egg whites and whip them up until they form stiff peaks with a hand mixer in another bowl. Use a spatula to gently fold them into the batter, along with the diced apple and oats. Cover the batter and let it sit overnight.