1. Preheat oven to 200 degrees. Heat waffle iron. Whisk together flour, oats, brown sugar, baking powder, baking soda, and salt in a large bowl. In another bowl, whisk together yolks, buttermilk, butter, and vanilla; stir into flour mixture.

2. Beat egg whites in a separate bowl until peaks are stiff but not dry. Fold into batter.

3. Coat waffle iron with cooking spray. Pour in batter, spreading almost to edges. Close lid; cook until waffles are golden, 3 to 5 minutes (or as indicated on waffle iron). Transfer to a baking sheet; keep warm in oven while cooking remaining batches. Serve warm, with Spicy Maple Butter and syrup.