01 -
Fill a large shallow bowl or baking dish with cold water and a generous amount of ice cubes. Transfer to the freezer until needed.
02 -
Combine half and half with instant espresso powder in a small bowl. Stir until the espresso is fully dissolved.
03 -
In a medium saucepan over low heat, combine the marshmallows with the half and half espresso mixture. Stir constantly until the marshmallows are fully melted, about 10 minutes. Remove from heat.
04 -
Remove the ice bath from the freezer. Place the saucepan into the ice bath and stir the melted marshmallow mixture until it cools to room temperature.
05 -
Add Irish whiskey to the cooled marshmallow mixture and mix until well combined. Remove the saucepan from the ice bath.
06 -
Gently fold the thawed whipped topping into the marshmallow mixture until thoroughly incorporated.
07 -
Transfer the filling into the prepared graham cracker crust. Cover and refrigerate for at least 4 hours or overnight to set completely.
08 -
Before serving, adorn the surface with whipped cream swirls and a light dusting of unsweetened cocoa powder if desired. Serve cold.