Preheat the oven to 350 F. Line an 8x8 pan with parchment paper and spray lightly with cooking spray. Use clothespins to keep the parchment paper in place if needed.
Warm the ¼ cup peanut butter and butter in a microwave safe vessel for 30 seconds.
Mix the white and brown sugars in a stand mixer bowl. Add in the melted butter/peanut butter combo. Mix on low speed to combine.
Add in the egg and vanilla, mix for another 30 seconds until combined.
In the mixing bowl, add in the baking powder, salt, flour, and cocoa powder. Mix on low speed until just combined. Do not over mix.
Pour the brownie mix into the prepared pan and use a spatula to even out the mix and spread it into all corners of the pan.
Warm up the ⅓ cup of peanut butter and the ⅓ cup of jelly in separate containers, for 15-20 seconds. It should be viscous, but not totally liquidy.
Use a spoon to randomly drop blobs of jelly and peanut butter across the top of the brownie mixture. Then use a butter knife to lightly swirl everything together artistically, but don't overdo it.
Bake for 30 minutes. Remove from oven, let cool for 10 minutes, and use a clean knife to slice.