Begin by preheating your oven to 350°F (175°C). Line a baking sheet with parchment paper or a silicone baking mat to ensure your cookies bake evenly and don’t stick.
In a large mixing bowl, combine the softened butter, white sugar, and brown sugar. Using a hand mixer or stand mixer, beat on medium speed until the mixture is light and fluffy, about 2-3 minutes.
Mix in the peanut butter until well combined. Then add the egg and vanilla extract, beating until the mixture is smooth and creamy.
In a separate bowl, whisk together the all-purpose flour, baking soda, and salt. Gradually add the dry ingredients to the wet mixture, mixing on low speed just until incorporated. Avoid overmixing to keep your cookies tender.
Gently fold in the peanut butter chips, half of the Reeses Pieces candy, and the chopped mini peanut butter cups. Save the remaining Reeses Pieces for topping the cookies just before baking.
Using a cookie scoop or tablespoon, drop dough balls onto the prepared baking sheet, spacing them about 2 inches apart. Press a few of the reserved Reeses Pieces candies onto the top of each cookie for a colorful, crunchy finish.
Bake in the preheated oven for 10-12 minutes, or until the edges are lightly golden but the centers still look soft. This ensures a chewy texture once cooled.
Allow the cookies to cool on the baking sheet for 5 minutes before transferring them to a wire rack to cool completely. This helps them set perfectly without breaking apart.