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 flour, cocoa powder, baking powder, and salt until evenly distributed.
03 - In a separate 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 wet mixture until just combined, being careful not to overmix.
05 - Fold chopped nuts and chocolate chips into batter until evenly distributed.
06 - Spoon batter evenly into prepared muffin cups, filling each about three-quarters full.
07 - Bake for 18 to 20 minutes, or until a toothpick inserted into the center comes out with a few moist crumbs.
08 - Allow brownie bites to cool in tin for 5 minutes, then transfer to a wire rack to cool completely.