1. Preheat the oven to 375 degrees F. Line a baking sheet with parchment paper or a silicone baking mat and set aside.
2. In a medium bowl, whisk together the flour, baking powder, baking soda, and salt. Set aside. Combine butter and sugars in the bowl of a stand mixer. Beat until smooth and creamy, about two minutes. On low, add in egg and vanilla extract. Beat until combined.
3. Slowly add in the dry ingredients. Stir in the oats, cereal, chocolate chips, and Butterfinger chunks. Don’t over mix. You don’t want to crush the cereal too much.
4. Scoop dough into balls, about a tablespoon each, and place on prepared baking sheet. Bake cookies for 10-12 minutes, or until edges are slightly brown, the centers should still be soft. Allow cookies to cool for 2-3 minutes on the baking sheet. Move cookies to a cooling rack and cool completely.