Fill a footed mug with hot water and let sit for 2 minutes to heat the glass.
While the mug sits, use a hand mixer to whip the heavy cream to medium peaks in a mixing bowl. Set aside.
Pour out the hot water and add the whiskey and brown sugar to the mug. Pour in the coffee, filling to about 1 inch shy of the rim of the glass. Stir until the sugar has melted
Top with a large dollop of the whipped cream. Serve immediately.
Notes
Using 2 tablespoons of heavy cream will yield about 1/4 cup of whipped cream. You can easily double or triple the amount of heavy cream used for making multiple cocktails. Keep any extra in an airtight container in the fridge for 2-3 days.