01 - Preheat oven to 350°F and grease a 24-cup mini muffin pan or line it with mini paper liners.
02 - In a medium bowl, whisk together the flour, cocoa powder, baking powder, and salt until evenly combined.
03 - In a large bowl, whisk melted butter and sugar until thoroughly blended. Add eggs and vanilla extract, whisking to a smooth, glossy consistency.
04 - Gently fold the dry ingredients into the wet mixture, mixing until just combined to avoid overmixing.
05 - Fold in mini chocolate chips and chopped nuts if desired.
06 - Spoon the batter evenly into the prepared mini muffin cups, filling each about three-quarters full.
07 - Bake for 13 to 15 minutes, or until the tops are set and a toothpick inserted comes out with a few moist crumbs.
08 - Allow to cool in the pan for 5 minutes before transferring to a wire rack to cool completely.