To make the mousse, place the chocolate, 1/3 cup cream and 1/4 tsp espresso powder in a heatproof bowl. Set the bowl in a skillet of barely simmering water. Stir frequently until the chocolate is completely melted and smooth. Remove the bowl from the skillet, stir in the whiskey and set aside. (You can use a double boiler instead of the bowl and skillet.).
In a heatproof medium bowl, whisk the eggs with 1 TB water and 2 TB sugar until well blended. Set the bowl in the skillet and whisk the eggs constantly (to prevent from scrambling) over hot (not simmering) water until they register 160 degrees on a thermometer. Remove the bowl from the skillet and beat at high speed with an electric mixer until the eggs have a texture like softly whipped cream, 3--4 minutes.
Fold one-quarter of the eggs into the chocolate. Scrape the chocolate mixture over the remaining whipped eggs and continue to fold just until evenly incorporated. Divide the mousse among 6--8 ramekins. Chill at least 1 hour, or unitl set, before serving.
In a chilled mixing bowl with chilled beaters, beat the remaining 2/3 cup of cream with the vanilla, the remaining 4 tsp sugar and the remaining 1 1/4 tsp espresso powder until nearly stiff. Top each mousse with a dollop of cream before serving.