Fill an Irish coffee mug with warm water and allow the water to warm up the glass.
Discard the water and pour the brewed coffee into the warmed mug. Add the Irish whiskey and brown sugar. Stir until the sugar is dissolved.
Use a whisk to slightly whip the heavy cream until it is bubbly but still pourable. Gently pour the cream over the back of a spoon on top of the coffee. If desired, you can whip the heavy cream until it is firm and dollop it onto the coffee.
Recipe Tips
It is important to keep the layers separated in the coffee. This way the person will get the experience of tasting the hot coffee through the cool layer of cream.