Preheat the oven to 350°F and line a baking sheet with parchment paper.
Using a hand or standing mixer, beat egg slightly. Then add granulated sugar, baking soda and vanilla until thoroughly combined. Beat in the peanut butter. Consistency will be similar to fudge.
Roll into 1 inch balls, place onto baking sheet. Add extra granulated sugar to plate, then dip fork into sugar. Flatten cookie in crisscross pattern with the back of the fork.
Bake for 12-15 minutes, until lightly set, they will fully set when cooled. Transfer to a wire rack to finish cooling.