Combine the hot water and brown sugar in a mug. Stir together until the brown sugar is melted. Stir in the whiskey and espresso. Top with several dollops of the whipped cream. Serve immediately with a spoon.
Lemon-Vanilla Whipped Cream:
Add the heavy cream, sugar, vanilla and lemon zest to a stand mixer fitted with the whisk attachment. Whip just until soft peaks form.