Prepare the coffee flavor: In a small bowl, dissolve the instant coffee granules in 1 tablespoon of hot water. Set aside to cool.

Whip the cream: In a large mixing bowl, beat the heavy cream with an electric mixer until soft peaks form. Gradually add the powdered erythritol, vanilla extract, and cooled coffee mixture. Continue whipping until the cream forms stiff peaks.

Add the Irish whiskey: Gently fold in the Irish whiskey or sugar-free Irish cream syrup, making sure it is evenly incorporated into the whipped cream mixture.

Chill the mousse: Spoon the mousse into individual serving glasses or bowls. Cover and refrigerate for at least 1 hour to let the flavors meld and the mousse to firm up.

Garnish and serve: Before serving, dust the top with unsweetened cocoa powder or garnish with sugar-free chocolate shavings for extra indulgence. Serve chilled and enjoy!