Melt chocolate 8 ounces of chocolate, cocoa powder, espresso powder, water and Kahlua or brandy in a bowl in a double boiler or over a pan filled with barely simmering water, stirring frequently until smooth. Remove from heat.
Whisk egg yolks, 1 1/2 teaspoons sugar and salt in a medium bow until mixture lightens in color and thickens slightly, about 30 seconds.
Pour a small amount of melted chocolate into egg mixture and whisk, continue adding and whisking in chocolate until combined.
Meanwhile, in a clean mixing bowl, beat egg whites at medium low speed until frothy, 1 to 2 minutes. Add remaining 1 1/2 teaspoons sugar, increase mixer speed to medium high, and beat until soft peaks form.
Using whisk, stir about one-quarter of beaten egg whites into chocolate mixture to lighten it; gently fold in remaining egg whites with rubber spatula until a few white streaks remain.
In now empty bowl, whip heavy cream at medium speed until it begins to thicken, about 30 seconds. Increase speed to high and whip until soft peaks form, about 15 seconds more.
Add remaining chocolate chips.
Using rubber spatula, fold whipped cream into mousse until no white streaks remain. Transfer into a bowl, cover and chill.