01 - Preheat oven to 350°F. Grease a 24-cup mini muffin tin or line with mini paper liners.
02 - In a medium bowl, whisk together the flour, cocoa powder, baking powder, and salt until well blended.
03 - In a large bowl, whisk melted butter and sugar until glossy and combined. Add eggs one at a time, whisking thoroughly after each addition. Stir in vanilla extract.
04 - Gently fold dry ingredients into the wet mixture until just combined. Avoid overmixing to maintain fudgy texture.
05 - Fold in chopped nuts and chocolate chips if desired until evenly distributed throughout batter.
06 - Spoon batter evenly into prepared muffin cups, filling each about 3/4 full.
07 - Bake for 18–20 minutes until a toothpick inserted into center comes out with a few moist crumbs.
08 - Let brownie bites cool in tin for 5 minutes, then transfer to wire rack to cool completely before serving.