Preheat your oven to 350°F (175°C). Line a 9x13-inch baking pan with parchment paper, leaving some overhang to make removing the brownies easier later.
In a medium bowl, whisk together the Dutch-processed cocoa, instant espresso (if using), and boiling water until smooth. Stir in the chopped unsweetened chocolate until melted and combined.
In a large mixing bowl, combine the melted unsalted butter and vegetable oil. Add the eggs, egg yolks, and vanilla extract, whisking until well combined. Next, stir in the prepared chocolate mixture.
In another bowl, whisk together the sugar, all-purpose flour, and salt. Gradually fold the dry ingredients into the wet mixture until just combined. Be careful not to overmix.
Gently fold in the bittersweet chocolate pieces until evenly distributed.
Pour the brownie batter into the prepared baking pan and spread it evenly. Bake in the preheated oven for 25-30 minutes, or until a toothpick inserted into the center comes out with a few moist crumbs.
While the brownies are baking, make the mint filling. In a medium bowl, beat together the unsalted butter and cream cheese until creamy. Add the green crème de menthe and powdered sugar gradually, mixing until smooth. Add a pinch of salt to taste.
Once the brownies have cooled in the pan for about 10 minutes, spread the mint filling evenly over the top. Allow the brownies to cool completely in the pan.
In a small saucepan over low heat, combine the heavy cream and unsalted butter, stirring until melted. Remove from heat and add the dark chocolate and creme de cacao, stirring until smooth and glossy.
Pour the ganache over the cooled mint filling and spread it evenly. Allow the ganache to set for at least 30 minutes before slicing into squares.