01 - Preheat oven to 350°F. Line an 8-inch square baking pan with parchment paper, leaving an overhang for easy removal.
02 - Melt butter in a medium saucepan or microwave. Whisk in sugar, eggs, and vanilla. Stir in cocoa powder, flour, salt, and baking powder until just combined. Spread batter evenly in prepared pan.
03 - Bake for 25–30 minutes, or until a toothpick inserted in the center comes out with a few moist crumbs. Let cool completely in the pan.
04 - Beat softened butter until smooth. Gradually add powdered sugar, milk, and peppermint extract, beating until light and fluffy. Mix in green food coloring until desired shade is reached.
05 - Spread the mint cream evenly over the cooled brownie base. Refrigerate for 30 minutes.
06 - Place chocolate chips and butter in a heatproof bowl. Heat cream until just simmering and pour over the chocolate; let sit 2 minutes, then stir until smooth.
07 - Pour ganache over the mint layer and spread evenly. Chill brownies at least 30 minutes before slicing.
08 - Lift brownies from pan using parchment, cut into squares, and serve.