01 - Preheat oven to 350°F. Line an 8x8 inch baking pan with parchment paper, allowing overhang on sides for easy removal.
02 - Whisk melted butter and granulated sugar in a bowl until blended. Add eggs and vanilla extract, mixing until smooth. Sift in flour, cocoa powder, and salt. Fold gently until just combined, being careful not to overmix.
03 - Pour batter into prepared pan, spreading evenly. Bake for 25-30 minutes until a toothpick inserted in center comes out with moist crumbs. Cool completely in pan before proceeding.
04 - Beat softened butter and powdered sugar until fluffy. Add milk, peppermint extract, and green food coloring if using. Continue beating until smooth and evenly colored. Spread evenly over cooled brownie base.
05 - Refrigerate pan for 20 minutes to set mint cream before adding ganache.
06 - Combine chocolate chips and butter in a heatproof bowl set over a pot of simmering water, creating a double boiler. Stir continuously until melted and smooth. Remove from heat and let cool slightly.
07 - Pour ganache over mint layer, spreading evenly to cover. Chill for at least 20 minutes until ganache is set. Lift brownies from pan using parchment edges. Cut into 16 squares with a sharp knife, wiping blade clean between cuts for clean edges.