01 - Preheat the oven to 350°F. Lightly grease a 24-cup mini muffin pan or line with paper liners.
02 - In a medium bowl, whisk together the flour, cocoa powder, baking powder, and salt until evenly distributed.
03 - In a large bowl, whisk the melted butter and granulated sugar until well combined. Add eggs and vanilla extract, whisking until smooth.
04 - Gradually fold the dry ingredient mixture into the wet mixture until just combined, taking care not to overmix.
05 - Gently fold in the semi-sweet chocolate chips and optionally the chopped walnuts or pecans.
06 - Divide the batter evenly into the prepared mini muffin cups, filling each about three-quarters full.
07 - Bake for 12 to 15 minutes or until the tops are set and a toothpick inserted in the center comes out with moist crumbs.
08 - Allow the brownie bites to cool in the pan for 5 minutes before transferring them to a wire rack to cool completely.