Add the brown sugar to a heatproof mug. Pour in the hot coffee and stir until the sugar has completely dissolved.
Stir in the Irish whiskey.
Lightly whip the heavy cream until it thickens slightly but is still pourable. Slowly pour it over the back of a spoon so it gently floats on top of the coffee.
Serve immediately and enjoy.
Notes
Use a medium or dark roast coffee for the best flavor.
Whip the cream just until it's thickened but still pourable.
Pour the cream over the back of a spoon so it floats on top.
Choose a smooth Irish whiskey for the best results.