Preheat oven to 350°F. Grease 3 baking sheets. Beat peanut butter and sugar in a large bowl with an electric mixer set at medium speed until well combined, about 1 minute.
Beat egg in a small cup with a fork. Add egg to peanut butter mixture in bowl. Add baking soda. Beat until well mixed.
Roll teaspoonfuls of dough into balls. Arrange dough balls 1 inch apart on prepared baking sheets. Put sugar on a plate. Dip fork tines in sugar and press onto the cookie ball in a criss cross pattern.
Bake cookies until puffed and golden, about 10 minutes. Cool on baking sheets for 2 minutes. Remove; cool completely.