01 - Preheat your 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.
03 - In a separate large bowl, whisk the melted butter and sugar until glossy and combined. Add eggs one at a time, whisking well after each addition, then stir in the vanilla extract.
04 - Gently fold the dry ingredients into the wet mixture until just combined—do not overmix.
05 - Fold in the chopped nuts and chocolate chips, if using.
06 - Spoon the batter evenly into the prepared muffin tin, filling each cup about 3/4 full.
07 - Bake for 18–20 minutes, or until a toothpick inserted into the center comes out with a few moist crumbs.
08 - Allow the brownie bites to cool in the tin for 5 minutes, then transfer to a wire rack to cool completely.