01 - Preheat oven to 350°F. Line an 8x8-inch baking pan with parchment paper, allowing overhang on sides for easy removal.
02 - In a medium saucepan, melt butter over low heat. Remove from heat and whisk in sugar, eggs, and vanilla until smooth. Stir in cocoa powder, flour, salt, and baking powder until just combined.
03 - Spread batter evenly in prepared pan. Bake for 25 to 30 minutes, or until a toothpick inserted in center comes out with a few moist crumbs. Cool completely in pan.
04 - In a medium bowl, beat softened butter until creamy. Gradually add powdered sugar, mixing until smooth. Add heavy cream, peppermint extract, and green food coloring. Beat until light and fluffy. Spread evenly over cooled brownies.
05 - Refrigerate brownies for at least 30 minutes until mint cream is set.
06 - Place chocolate chips and butter in a heatproof bowl. Heat heavy cream in a small saucepan until just simmering. Pour over chocolate and let sit for 2 minutes. Stir until smooth and cool slightly.
07 - Pour ganache over mint layer and spread evenly. Refrigerate for at least 30 minutes until ganache is completely set. Lift from pan using parchment overhang, cut into 16 equal squares, and serve.