This cocktail is always served in an Irish coffee cup, which is clear to show off the light cream against the dark coffee and has a handle to prevent burns from a hot glass. Warm the glasses by filling them with hot water and letting them sit for a few minutes before pouring out the water.
1/4 cup packed dark brown sugar
2 cups strong hot coffee
3/4 cup Irish whiskey, such as Jameson
3/4 cup heavy cream
Combine the brown sugar and 2 Tbs. water in a 1-quart saucepan and stir over low heat until the sugar is just dissolved. You’ll have 1/4 cup of syrup; depending on how sweet you like your Irish coffee, you may not need it all.
Pour 1/2 cup of the coffee, 3 Tbs. of the whiskey, and 2 to 3 tsp. of the brown sugar syrup into each of 4 warmed 6-oz. glass Irish coffee mugs.
In a medium bowl, beat the cream with a whisk just until it’s frothy and slightly thickened but does not yet hold a peak, about 1 minute. With a soup spoon, float about 3/4 inch of the lightly whipped cream on top of each coffee and serve immediately.