Preheat oven to 350 ℉. Line a baking sheet with parchment paper.
Mix the peanut butter, white sugar, and egg together until combined and smooth. Roll into 1 inch balls. Flatten with a fork creating a criss-cross pattern.
Bake until cookies are slightly brown on the bottom, about 6 - 8 minutes.
Remove from oven and allow to cook and slightly harden for 10 minutes.