01 - Preheat oven to 350°F. Line a 9x9 inch baking pan with parchment paper.
02 - Whisk together melted butter, granulated sugar, and brown sugar until smooth. Beat in eggs and vanilla extract.
03 - Sift in flour, cocoa powder, and salt. Stir until just combined. Fold in chocolate chips.
04 - Pour batter into prepared pan and smooth the top. Bake for 30-35 minutes, or until a toothpick comes out with moist crumbs. Let cool completely in the pan.
05 - Beat softened butter until creamy. Gradually add powdered sugar, milk, and peppermint extract. Beat until fluffy. Add green food coloring if desired.
06 - Spread the mint layer evenly over cooled brownies. Refrigerate for 20 minutes to set.
07 - Melt chocolate chips and butter together, stirring until smooth. Let cool slightly, then pour over the mint layer.
08 - Refrigerate for at least 30 minutes until the topping sets. Lift brownies from pan and cut into squares.