Preheat the oven: Set it to 350°F (175°C). Line a baking sheet with parchment paper.

Mix the wet ingredients: In a medium bowl, stir 1 cup creamy peanut butter with 1/2 cup granulated sugar and 1/4 cup brown sugar (if using) until smooth. Add 1 large egg and 1 teaspoon vanilla extract. Stir until fully blended.

Add the dry ingredients: Sprinkle in 1/2 teaspoon baking soda and 1/4 teaspoon salt. Stir just until no dry bits remain. If using add-ins, fold in up to 1/2 cup.

Portion the dough: Scoop tablespoons of dough and roll into balls. Place them 2 inches apart on the baking sheet.

Press and pattern: Gently press each ball with a fork to make a crisscross pattern. This flattens the cookies so they bake evenly.

Bake: Bake for 8–10 minutes, until the edges are set and the tops look slightly cracked. They should still be soft in the center.

Cool: Let cookies rest on the baking sheet for 5 minutes, then transfer to a rack to cool completely. They firm up as they cool.