Preheat your oven to 350°F (175°C) and grease a 9x13 inch baking pan. In a medium saucepan, melt together butter with cocoa powder and sugar over low heat, stirring until smooth. Once combined, add salt, eggs, and vanilla extract, mixing well. Gradually incorporate all-purpose flour until just blended. Pour the rich brownie batter into the prepared pan and bake for 30-35 minutes, or until a toothpick inserted in the center comes out clean. Allow to cool completely before frosting.

While the brownies are cooling, prepare the mint frosting. In a mixing bowl, beat together softened butter and powdered sugar until creamy. Gradually add mint extract and heavy cream, mixing until you reach a smooth, spreadable consistency. If desired, tint your frosting with green food coloring for a pop of color. Once the brownies are fully cooled, spread the vibrant mint frosting evenly over the top.

In a microwave-safe bowl, combine semi-sweet chocolate chips and a bit of butter. Microwave in short increments of 30 seconds, stirring in between, until smooth and fully melted. If you prefer a thinner consistency, add a splash of canola oil. Carefully pour this luscious chocolate over the mint frosting, using a spatula to spread it evenly across the surface. Allow the brownies to set at room temperature until the chocolate layer is firm before cutting into squares.