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.

In the morning, the batter will be very thick. This is perfect. Heat up an electric griddle to 350 or a griddle pan over medium high heat on the stove. Lightly grease the griddle with butter. Scoop the batter onto the griddle in the size pancakes you desire, cooking about 6-8 pancakes per batch. Let them cook for 3-4 minutes on each side to get them puffy and golden. Serve them as you cook them with apple slices and maple syrup on top! Enjoy!