Preheat the oven to 350°F. Line a baking sheet with parchment paper or a silicone baking mat and set aside.
In a large mixing bowl (or the bowl of a stand mixer), add 1 cup smooth peanut butter and 1 cup light or dark brown sugar.
Mix on medium speed about 30 seconds, until the peanut butter and sugar are combined and the mixture loosens slightly. Scrape down the bowl as needed.
Add 1 large egg and continue mixing on medium until the dough is smooth and homogenous, about 20–30 seconds.
Add 1 cup granola cereal and ½ cup semi-sweet chocolate chips. Mix on low speed just until the granola and chips are evenly incorporated; avoid overmixing.
Using a 1½-tablespoon scoop or measuring spoon, drop rounded scoops of dough onto the prepared baking sheet, spacing them about 2 inches apart.
Bake in the preheated oven for 9–10 minutes, until the edges are set and the tops look slightly firm but the centers are still a bit soft.
Remove the baking sheet from the oven and let the cookies cool on the sheet for 5–7 minutes (they will be fragile while warm).
After 5–7 minutes, transfer the cookies to a wire rack to cool completely.
Once cooled, store the cookies in an airtight container for up to 5 days.