In a large mixing bowl, combine the heavy whipping cream, powdered sugar, and vanilla extract. Whip the mixture with an electric mixer on medium-high speed until stiff peaks form. This should take about 3-4 minutes.
In another bowl, mix the brewed coffee with the cocoa powder and instant coffee granules (if using) until well combined.
Take a chocolate wafer cookie, dip one side briefly into the coffee mixture to soak, then layer it on the bottom of a 9x13 inch baking dish. Repeat with more cookies, forming a base layer.
Spread a layer of the whipped cream mixture over the cookies in the dish, then sprinkle a portion of chocolate chips on top.
Repeat the layering process using the soaked cookies, whipped cream mixture, and chocolate chips until you run out of ingredients, finishing with a layer of whipped cream on top.
Cover the dish with plastic wrap and refrigerate for at least 6 hours, or overnight for best results to allow the flavors to meld together and the cookies to soften.
When ready to serve, remove the dish from the refrigerator. Use a spatula to smooth the top, if necessary, and sprinkle some additional chocolate chips on top for decoration.
Cut into squares, serve chilled, and garnish with fresh mint leaves if desired.
Notes
Serve each square on a dessert plate, topped with a dollop of whipped cream and a dusting of cocoa powder for an elegant touch.