Preheat and prep: Heat your oven to 350°F (175°C).
Line a baking sheet with parchment paper.
Mix the base: In a medium bowl, stir together peanut butter, sugar, egg, and vanilla until smooth and glossy.
Add leavening and salt: Sprinkle in baking soda and salt. Mix until fully combined. The dough will be thick and scoopable.
Fold in extras: If using chocolate chips or chopped peanuts, fold them in now.
Shape the dough: Scoop heaping tablespoon portions and roll them into balls.
Place them 2 inches apart on the baking sheet.
Crisscross pattern: Gently press each ball with a fork in a crisscross pattern to flatten slightly to about 1/2 inch thick.
Bake: Bake for 9–11 minutes, until the edges look set and the tops are slightly crackly. The centers may look soft—that’s perfect.
Cool: Let cookies rest on the baking sheet for 5 minutes, then transfer to a wire rack to cool completely. They firm up as they cool.