Warm the glass (optional but recommended): Fill a heatproof coffee mug with hot water and let sit for 1 minute. Discard the water before building the drink.
Sweeten the coffee: Add the brown sugar and a pinch of sea salt to the mug. Pour in the hot coffee and stir until the sugar is fully dissolved.
Add the whiskey: Stir in the Irish whiskey until fully incorporated.
Top with cream: Gently float the lightly whipped heavy cream over the back of a spoon so it rests on top of the coffee.Tip: The cream should be softly whipped, thickened but still pourable, so it floats beautifully while remaining silky and smooth. Garnish and serve: Finish with a light dusting of chocolate shavings or cocoa powder. Serve immediately.