Put the walnuts in a blender container. Blend and set aside.

In the blender container, place the egg white (store the yolk in the fridge and use it for another meal within a few days), peanut butter, and grated zest of a scalded lemon. Blend to combine the ingredients. Add the crushed nuts and mix thoroughly.

Lay out about 1 teaspoon of the mixture (for 1 cookie) on a baking tray lined with parchment paper. Bake in an oven preheated to 180°C (356°F) for about 12-15 minutes, checking occasionally to ensure they don't overbrown. Remove when golden.

Enjoy warm or cold.