01 - Preheat oven to 350°F. Line an 8-inch square baking pan with parchment paper, allowing overhang on sides for easy removal later.
02 - Place butter in a microwave-safe bowl and melt completely. Whisk in sugar until incorporated, then add eggs and vanilla extract. Mix until smooth and glossy.
03 - Sift flour, cocoa powder, and salt directly into the wet mixture. Fold gently until just combined—do not overmix. Stir in chocolate chips.
04 - Spread batter evenly into prepared pan. Bake for 25-30 minutes until a toothpick inserted comes out with moist crumbs, not wet batter. Cool completely in pan before proceeding.
05 - Beat softened butter and powdered sugar together until smooth and creamy. Add milk, peppermint extract, and food coloring if using. Continue beating until fluffy and spreadable.
06 - Spread mint mixture evenly over completely cooled brownies. Refrigerate for 20 minutes to set before adding ganache.
07 - Heat heavy cream in a small saucepan until steaming but not boiling. Pour over chocolate chips in a heatproof bowl. Let sit for 1 minute, then stir continuously until smooth and glossy.
08 - Pour ganache over chilled mint layer, spreading evenly with an offset spatula. Refrigerate for at least 30 minutes until ganache is set. Lift from pan using parchment overhang and slice into 16 squares.