Put Caster Sugar (1 cup), Egg (1) and Peanut Butter (1 cup) into a mixing bowl. Use an electric mixer to beat everything together until it's combined and smooth.
Take a teaspoonful of cookie dough mixture and roll it in your hand to make a little ball. Put the ball on a baking tray lined with some non-stick baking paper. Use a fork to gently press down the ball. Finish the rest in this way.
Preheat the oven to 180 degrees C (350 degrees F). Put the cookies in for about 10 minutes or until the cookies are firm and golden. Once out of the oven, leave the tray for at least 5 minutes so they can firm up a little bit before transferring them to a wire rack to cool completely. Serve and enjoy!