Start by preheating your oven to 350°F (175°C). Line a baking sheet with parchment paper or a silicone baking mat.
In a large mixing bowl, combine the peanut butter, brown sugar, granulated sugar, eggs, and vanilla extract. Mix until the ingredients are well combined and smooth.
Add the rolled oats, baking soda, and salt to the wet mixture. Stir until everything is well incorporated. If you’re adding chocolate chips or raisins, fold them into the dough at this point.
Using a tablespoon or a cookie scoop, drop rounded balls of dough onto the prepared baking sheet, spacing them about 2 inches apart.
Bake in the preheated oven for 10-12 minutes, or until the edges are lightly golden. The cookies may look slightly under-baked in the middle, but they will set as they cool.
Allow the cookies to cool on the baking sheet for about 5 minutes before transferring them to a wire rack to cool completely.