Preheat the oven to 350°F. Grease an 8x8-inch square pan with cooking spray, and line it with parchment paper, leaving extra over the sides for easy removal of the brownies.

Unwrap and roughly chop the Andes mint chocolate; set aside.

In a medium bowl, whisk together the dry ingredients: flour, cocoa powder, espresso powder, and salt. Set aside.

In a separate microwave-safe bowl, combine the butter, oil, brown sugar, and ½ cup of granulated sugar. Microwave for 30 seconds, stir, then microwave for another minute, stirring every 30 seconds, until the butter is fully melted and the sugar dissolves. Let it cool to room temperature.

In another bowl, beat the eggs, egg yolk, and the remaining ½ cup of granulated sugar on medium speed using a hand mixer or whisk for 4-5 minutes, until the sugar is dissolved and the mixture turns pale.

Add the cooled butter mixture to the egg mixture and mix until just combined.

Using a spatula, fold in the dry ingredients in batches, mixing until just incorporated. Be careful not to overmix. Gently fold in the dark chocolate chips and most of the chopped Andes mint chocolate, reserving some for the top.

Pour the brownie batter into the prepared pan, tapping it on the counter to ensure even spreading. Sprinkle the reserved Andes mint chocolate on top.

Place the pan on the top rack of the oven and bake for 27-30 minutes, until a toothpick inserted in the center comes out with moist crumbs for that perfect fudgy texture.

Let the brownies cool in the pan for 10 minutes, then use the parchment overhang to lift them out onto a cooling rack. Once fully cooled, slice into 8 or 12 squares and enjoy!