Fill a 6-ounce heat-proof glass with very hot water to preheat it. Wait about a minute, then discard the water.
Place 2 sugar cubes in the warm glass, then add 6 ounces of hot brewed coffee. Stir until the sugar is completely dissolved.
Pour the whiskey in and stir. Slowly add the lightly whipped heavy cream over the back of a spoon so it floats on top of the coffee. Serve immediately.