Preheat your oven to 350°F (175°C). Prepare a 9×13-inch pan by greasing it thoroughly. Follow the instructions on the brownie mix box, adding espresso powder if desired. Bake until a toothpick comes out with a few moist crumbs, about 20-25 minutes. Allow brownies to cool completely.

Once cooled, slice the brownie base horizontally into two equal layers using a long serrated knife.

In a chilled mixing bowl, add heavy cream, powdered sugar, cocoa powder, and vanilla extract. Beat on medium-high speed until stiff peaks form, around 3-4 minutes.

Prepare the dish by lining it with parchment paper. Place one half of the brownie layer in the dish and spread half of the whipped cream over it. Add the second brownie layer on top, followed by the remaining whipped cream.

In a saucepan, heat heavy cream over medium heat until steaming. Pour it over the chocolate chips in a bowl, let it sit for 2 minutes, then stir until smooth. Let cool for 5 minutes.

Pour the cooled ganache over the top layer of whipped cream, using a spatula to spread it evenly. Cover with plastic wrap and refrigerate for at least 4 hours, preferably overnight.

To serve, lift the cake out of the dish using the parchment paper. Cut into squares using a sharp knife. Optionally garnish with chocolate shavings or fresh berries before serving.