Preheat a heatproof glass or mug with hot water, then empty it
Add 1 to 1 1/2 teaspoons brown sugar
Pour in 1 1/2 to 2 ounces Irish whiskey
Add 4 to 6 ounces hot strong coffee
Stir until the sugar dissolves
Lightly whip 1 to 2 ounces heavy cream until just thickened
Gently float the cream on top by pouring it over the back of a spoon
Serve immediately without stirring