How to Make It
Prepare the Brownies: Preheat oven to 350°F. Combine butter and chocolate in a small saucepan over medium-low, and cook, stirring constantly until melted and combined. Set aside to cool slightly.
Combine both sugars with slightly cooled butter mixture in the bowl of a stand mixer, and beat on medium speed until well blended. Add eggs, 1 at a time, and beat until incorporated. Add vanilla and salt, and beat to combine. With mixer on low, add flour, and beat until just combined.
Stir chopped Andes mint pieces into batter. Pour batter into lightly greased 13- x 9-inch baking dish, and bake in preheated oven until a toothpick inserted in center comes out clean, about 20 minutes. Cool in pan on wire rack 20 minutes.
Prepare the Mint Filling: Beat together butter, cream cheese, and salt in bowl of a stand mixer until smooth. Add powdered sugar and milk, and beat until smooth. Add extract and 1 to 3 drops of food coloring until desired color is achieved; stir to combine. Spread Mint Filling over cooled Brownies, and chill 30 minutes.
Prepare the Chocolate Ganache: Place chocolate chips in a medium bowl. Heat heavy cream in a small saucepan until just before it boils; pour over chocolate chips, and let stand 1 minute. Stir until completely melted and smooth. Add corn syrup, and stir until smooth. Pour Chocolate Ganache over chilled Mint Filling, spreading to edges. Top with sliced Andes mint pieces. Chill at least 1 hour before serving.