Preheat oven to 325°F. Prepare an 8 inch or 9 inch baking dish by spraying with cooking spray and lining with parchment paper. Set aside.
Using a double boiler, melt the butter, chocolate, and baking chips (if using) together. Remove from heat. (You can also melt in the microwave. Heat at 50% power in 20 second increments, stirring in between.)
½ cup unsalted butter, 4 ounces unsweetened chocolate, ¼ cup Andes creme de menthe baking chips
Stir in the granulated sugar, vanilla and mint extracts until combined.
1¼ cups granulated sugar, 1 teaspoon vanilla extract, ½ teaspoon mint extract
Add the eggs in one at a time making sure they are well incorporated.
2 large eggs
Finally mix in the flour and salt and beat until smooth and combined.
½ cup all purpose flour, ¼ teaspoon salt
Pour the brownie batter evenly into the prepared pan and bake for about 25 to 30 minutes or until an inserted toothpick comes out with a few moist crumbs. Place on a wire rack to cool completely.