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 melted butter and sugar until smooth. Add eggs and vanilla extract; mix well.
03 - Sift in cocoa powder, flour, salt, and baking powder. Stir until just combined; do not overmix.
04 - Spoon batter evenly into the mini muffin cups, filling each about 2/3 full.
05 - Bake for 14-16 minutes, or until the tops are set and a toothpick inserted comes out with moist crumbs.
06 - Allow brownie bites to cool in the pan for 5 minutes, then transfer to a wire rack to cool completely.
07 - Beat butter until creamy. Gradually add powdered sugar, peppermint extract, and 1 tablespoon milk. Beat until smooth, adding more milk if needed for spreadable consistency. Tint with green food coloring.
08 - Pipe or spread a small dollop of mint frosting onto each cooled brownie bite. Decorate with chocolate sprinkles or mini chocolate chips if desired.