In a small bowl, dissolve the instant coffee granules in the hot water. Stir until completely dissolved and set aside to cool slightly (about 2 minutes).
In a medium mixing bowl, add the cold heavy whipping cream, powdered sugar, vanilla extract, and pinch of salt.
Using an electric hand mixer on medium speed, whip the cream mixture until it begins to thicken (about 2 minutes).
Gradually pour in the dissolved coffee mixture while continuing to whip.Continue beating until firm peaks form - the cream should hold its shape when the beaters are lifted (about 3-4 more minutes).
Spoon the coffee mousse into serving glasses or ramekins.
Refrigerate for at least 2 hours before serving for best texture and flavor.
Garnish with chocolate shavings, cocoa powder, or a sprinkle of instant coffee before serving if desired.