Place the rolled oats in a blender or food processor and pulse until they form a fine, flour-like consistency, which should take about 30 seconds. Transfer the freshly made oat flour to a large mixing bowl.

Whisk the baking powder, ground cinnamon, and salt into the oat flour until well combined. In a separate medium bowl, whisk together the milk, eggs, maple syrup, and vanilla extract until completely smooth.

Pour the wet ingredients into the dry ingredients, stirring gently with a spatula until just combined. Fold in the grated apple, being careful not to overmix the batter, and let it rest for 5 minutes to thicken up.

Heat a large non-stick skillet or griddle over medium heat and melt a small amount of the butter or coconut oil. Once the pan is hot and the fat is bubbling slightly, pour 1/4 cup portions of the batter onto the skillet.

Cook the pancakes for 2 to 3 minutes on the first side, until small bubbles begin to form on the surface and the edges look set. Flip carefully with a flat spatula and cook for another 1 to 2 minutes until the bottoms are golden brown and cooked through.

Transfer the cooked pancakes to a warm plate and repeat the process with the remaining batter, adding more butter to the pan as needed. Serve immediately in stacks, topped with warm maple syrup and a sprinkle of extra cinnamon.