Preheat oven to 350°F. Line a 13x9-inch pan with foil and spray the foil lightly with cooking spray. Set the prepared pan aside.

In a microwave-safe bowl, combine 1 cup butter and 6-ounce unsweetened chocolate. Microwave in 30-second intervals, stirring between intervals, until fully melted and smooth.

Stir 2 cups sugar, 1 teaspoon vanilla, and 1 teaspoon salt into the melted chocolate mixture.

Add 4 eggs and 1 1/4 cups flour to the bowl and mix until just incorporated and smooth.

Spread the brownie batter evenly into the prepared 13x9-inch pan. Bake 40–45 minutes, or until a toothpick inserted near the center comes out clean. Remove from oven and let the brownies cool completely in the pan on a wire rack.

While the brownies cool, make the mint frosting: beat 3/4 cup butter (softened) and 3 ounces cream cheese (softened) together until smooth.

Add 2 teaspoons mint extract, 5 drops green food coloring, and 3 cups powdered sugar to the butter–cream cheese mixture. Beat until the frosting is smooth and creamy.

Spread the mint frosting evenly over the cooled brownies. Place the pan in the refrigerator and chill for 30 minutes to firm the frosting.

In a microwave-safe bowl, combine 1/2 cup butter and 2 cups semi sweet chocolate chips. Microwave in 30-second intervals, stirring between intervals, until the chocolate and butter are fully melted and smooth.

Spread the melted chocolate mixture over the chilled mint frosting in an even layer. Return the pan to the refrigerator and chill 1–3 hours, or until the chocolate is set and the brownies are firm enough to cut.

Use the foil to lift the brownies from the pan, peel off the foil, cut into squares, and serve.