01 - Preheat oven to 350°F. Line an 8-inch square baking pan with parchment paper, ensuring overhang on sides for easy removal.
02 - Melt butter in a mixing bowl. Whisk in sugar, eggs, and vanilla extract until thoroughly combined.
03 - Sift cocoa powder, flour, and salt into the wet mixture. Mix until just combined, being careful not to overmix.
04 - Fold in semisweet chocolate chips. Pour batter into prepared pan and spread evenly. Bake for 25-30 minutes until a toothpick inserted in the center comes out with a few moist crumbs. Cool completely before proceeding.
05 - Beat softened butter until creamy. Gradually add powdered sugar, milk, peppermint extract, and green food coloring if using. Mix until smooth and spreadable consistency is achieved.
06 - Spread the mint mixture evenly over the cooled brownies. Refrigerate for 20 minutes to set before adding chocolate topping.
07 - Melt chocolate chips and butter together using microwave or double boiler, stirring frequently until completely smooth and glossy.
08 - Pour chocolate topping over the chilled mint layer. Spread evenly and refrigerate until fully set, approximately 30 minutes. Cut into squares and serve chilled or at room temperature.