Preheat oven to 350 F (175 degrees C).
Mix peanut butter, sugar, and egg together in a bowl using an electric mixer until smooth and creamy.
Roll mixture into small balls and arrange on a baking sheet; flatten each with a fork, making a criss-cross pattern.
Bake in preheated oven for 10 minutes. Cool cookies on the baking sheet for 2 minutes before moving to a plate.