In a saucepan over medium heat, melt the butter and semi-sweet chocolate, stirring constantly, or melt in a microwave safe bowl in 30 second increments until melted and smooth. Remove from the heat, pour into a large mixing bowl and allow to cool slightly for 8-10 minutes.
Adjust the oven rack to the lower third position and preheat the oven to 350°F. Line an 8x8 or 9×9 inch square baking pan with aluminum foil or parchment paper, leaving an overhang on all sides to remove the brownies easily after baking. Set aside.
Once the chocolate and butter are cooled slightly, whisk in the granulated and brown sugar. Add the eggs, one at a time, whisking until smooth after each addition. Whisk in the vanilla then gently fold in the flour, cocoa powder, and salt. Be careful not to overmix.
Pour half of the batter into the prepared baking pan. Place the Andes mints on top of the batter in an even layer, then top your mints with the Hershey's Chocolate bars in an even layer. Pour the other half of the batter on top of the chocolate bars and smooth to even out the batter.
Bake for 35 minutes, or until the brownies begin to pull away from the edges of the pan.
Remove from oven and allow the brownies to cool completely in the pan set on a wire rack. Once cooled, lift the foil out of the pan using the overhang on the sides and cut into squares.
*The standard toothpick trick to test if your brownies are done will not work with this recipe. The Andes mints and Hershey's chocolate bars will melt and liquify while still hot, and your toothpick will not come out clean.