1. Preheat your oven to 350°F (175°C) and prepare a mini muffin tin by greasing it lightly or using paper liners.
2. In a medium bowl, sift together the flour, cocoa powder, baking powder, and salt. Set aside.
3. In a large bowl, whisk together the melted butter and granulated sugar until well combined.
4. Add the eggs one at a time to the butter mixture, beating well after each addition. Stir in the vanilla extract.
5. Gradually fold the dry ingredients into the wet mixture, stirring just until combined to avoid overmixing.
6. Spoon the batter into the prepared mini muffin tin, filling each cup about three-quarters full.
7. In a small bowl, mix the peanut butter and confectioners’ sugar until smooth. Drop a small dollop of the peanut butter mixture onto each brownie bite and use a toothpick or skewer to swirl it gently into the batter.
8. Bake in the preheated oven for 12-15 minutes, or until the brownie edges are set and a toothpick inserted into the center comes out with a few moist crumbs.
9. Allow them to cool in the pan for a few minutes before transferring to a wire rack to cool completely.

Remember, as my abuela always said, cooking is about feeling, so don’t stress about perfection—let your senses guide you.