Preheat oven to 375 degrees and line two baking sheets with parchment paper.
In a large saucepan over medium heat, melt the butter. Add the brown sugar and oats, stirring and cooking for about 2 minutes. Remove from heat and allow to cool a bit.
With a KitchenAid or hand mixer, beat egg whites until stiff, but not dry. Add to cooled saucepan with oats mixture and stir until combined.
Using a mini cookie (or ice cream) scoop, place cookies about 2 inches apart on baking sheet. Do not flatten, they will flatten themselves in the oven.
Bake for 7-10 minutes or until edges are light brown. Remove from oven and allow them to settle a bit before transfering to wire rack to cool completely (if you remove them too early, they might fall apart).