These unbelievably easy – and gluten-free – cookies have only three ingredients and are a great way to use up those extra mixed nuts hanging out in your pantry.
Position a rack in the middle of the oven and preheat to 300°F. Line a baking sheet with parchment.
Pulse the nuts in a food processor until coarsely chopped.
Beat the egg white in a medium bowl with an electric mixer until stiff peaks form, about 2 minutes. Gently fold in the sugar and nuts. Spoon leveled tablespoons of the batter onto the prepared baking sheet, about 12 cookies total.
Bake, rotating halfway through, until golden brown, 25 to 30 minutes. Cool completely on the baking sheet set on a wire rack.