- Preheat your oven to 350°F (175°C). 
- Line a baking sheet with parchment paper. 
- In a large mixing bowl, combine the peanut butter, granulated sugar, egg, vanilla extract, baking soda, and salt. Mix until well combined and smooth. 
- Gently fold in the mini Reese's Pieces or chopped Reese's Peanut Butter Cups. 
- Using a cookie scoop or tablespoon, drop rounded balls of dough onto the prepared baking sheet, spacing them about 2 inches apart. 
- Flatten each ball slightly with the back of a fork, creating a crisscross pattern if desired. 
- Bake in the preheated oven for 10-12 minutes, or until the edges are lightly golden. 
- Remove from the oven and let the cookies cool on the baking sheet for 5 minutes before transferring them to a wire rack to cool completely.