In a large bowl, whisk together the oat flour, sugar, baking powder, cinnamon and salt.
Make a well in the centre of the oat flour mixture and pour in the milk, egg yolks, and melted butter. Stir to combine.
In a separate glass, metal or ceramic bowl*, whisk together the egg whites to stiff peaks. Fold the egg whites into the batter.
Lightly grease a nonstick pan or griddle over medium low heat and pour about 1/4-1/3 cup of batter in to the pan. Spread the batter to form a 4 inch pancake. Two at a time should fit in a 12-inch skillet.
Cook the pancakes until golden, bubbles have appeared on the surface and the edges are beginning to set (about 2 minutes). Flip and cook until cooked through and brown on both sides. Repeat with remaining batter.
*You can purchase oat flour or make it yourself by pulsing about 3 cups of rolled oats in a food processor to a fine powder.*Use a glass, metal or ceramic bowl to beat egg whites, never plastic. Grease gets stuck in the scratches of plastic bowls and prevent the whites from getting foamy.