Begin by preheating your oven to 350°F (175°C). Grease an 8x8-inch baking pan and line it with parchment paper.

In a large mixing bowl, melt the butter and stir in the sugar until combined. Crack in the eggs one at a time, whisking well after each addition. Add the vanilla extract. In a separate bowl, sift together the flour, cocoa powder, baking powder, and salt. Gradually fold the dry ingredients into the wet mixture until smooth.

Pour the batter into the prepared pan and spread it evenly. Bake for 25-30 minutes. A toothpick inserted should come out with a few moist crumbs.

While the brownies cool, combine powdered sugar, milk, peppermint extract, and green food coloring for the frosting. Whisk until smooth. Adjust consistency as needed. Spread over cooled brownies and sprinkle with dark chocolate chips.