01 - Preheat oven to 350°F. Line an 8-inch square baking pan with parchment paper, leaving an overhang for easy removal.
02 - In a microwave-safe bowl, melt butter and chopped chocolate together in 30-second intervals, stirring until smooth. Cool slightly.
03 - Whisk in granulated sugar, eggs, and vanilla extract until glossy and well combined.
04 - Fold in flour and salt until just incorporated. Do not overmix.
05 - Pour batter into prepared pan and smooth the top. Bake for 25–30 minutes, or until a toothpick inserted comes out with moist crumbs. Let cool completely in the pan.
06 - In a bowl, beat softened butter with powdered sugar, milk, peppermint extract, and green food coloring until smooth and spreadable.
07 - Spread mint mixture evenly over cooled brownies. Chill in the refrigerator for 15 minutes.
08 - Melt chocolate chips with vegetable oil in the microwave in 20-second bursts, stirring until smooth.
09 - Pour melted chocolate over chilled mint layer and gently spread to cover. Refrigerate for at least 30 minutes to set. Lift brownies from the pan using parchment, cut into squares, and serve.