01 - Preheat oven to 350°F. Line an 8x8-inch baking pan with parchment paper, allowing overhang on edges for easy removal.
02 - Combine butter and semisweet chocolate chips in a heatproof bowl. Melt over simmering water or microwave in 30-second intervals, stirring until smooth. Let cool slightly.
03 - Whisk sugar into melted chocolate mixture. Add eggs one at a time, beating well after each addition. Stir in vanilla extract.
04 - Fold in flour and salt just until combined. Do not overmix. Spread batter evenly into prepared pan.
05 - Bake for 25-30 minutes until a toothpick inserted in center comes out with moist crumbs. Cool completely in pan on wire rack.
06 - Beat softened butter until fluffy. Gradually incorporate powdered sugar, milk, and peppermint extract. Beat until smooth and creamy. Add green food coloring to desired intensity.
07 - Spread mint cream evenly over completely cooled brownies. Refrigerate for at least 30 minutes until firm.
08 - Heat heavy cream until steaming but not boiling. Pour over chocolate chips and butter in a bowl. Let stand 2 minutes, then stir until completely smooth and glossy.
09 - Pour ganache over chilled mint layer. Spread evenly with offset spatula. Refrigerate 30-45 minutes until set.
10 - Lift brownies from pan using parchment overhang. Cut into 16 squares using a sharp knife warmed under hot water for clean edges.