Stir the butter and sugar until fluffy. In a separate bowl mix together the potato starch, baking powder, and grated lemon peel. Then alternate adding the egg and potato starch mixture to the butter and sugar.
Roll out small balls and place them on a baking tray lined with baking paper. Flatten the cookies a bit with your hand for smooth cookies, or with the back of a fork for textured cookies. Leave some space between each ball.
Bake the cookies in the middle of the oven for approximately 10 minutes until they are golden and crispy. Cool the cakes on a wire rack and store them in an airtight container.