Prepare a square 8x8 baking pan with parchment paper and set it aside. Preheat the oven to 350 F/180 C.
In a large mixing bowl, whisk together the sugar, brown sugar, eggs, egg yolk, and vanilla until light and fluffy, about 1-2 minutes.
In a small pot, melt the butter over low heat. Add the chocolate chips and stir until smooth.
Stream the hot melted butter and chocolate mixture into the egg and sugar bowl, whisking until just combined.
Fold in the flour, cocoa powder, espresso, and salt until almost combined and some flour streaks remain.
Add in the chopped andes mints and continue folding until just combined.
Pour the batter into the prepared baking pan.
Bake for 20-25 minutes or until the top is shiny, the edges are cracked, and a toothpick inserted into the center comes out smeared in chocolate.
Let the pan cool completely on a wire rack, then remove it from the pan.
Drizzle the top with chocolate and sprinkle with more chopped andes mints and enjoy!