Heat the oven: Preheat to 350°F (175°C). Line a baking sheet with parchment paper for easy cleanup.
Mix the dough: In a medium bowl, whisk the egg and sugar until combined.
Add the peanut butter and stir until smooth and thick. The dough should hold together and not look oily.
Scoop and shape: Use a tablespoon or small cookie scoop to portion 1 to 1.5-inch balls. Roll gently between your palms and place 2 inches apart on the baking sheet.
Make the crisscross: Press each dough ball with the tines of a fork in one direction, then again at a 90-degree angle to create the classic crisscross pattern. This flattens the cookies for even baking.
Bake: Bake for 9–11 minutes, until the edges are set and the tops look slightly dry. They’ll still be soft in the center.
Cool: Let cookies cool on the baking sheet for 5 minutes, then transfer to a rack to finish cooling. They firm up as they cool.