Melt the chocolate chips in a 2 1/2-qt. sauce pan over very low heat, stirring constantly. Add the coffee, liqueur and orange zest. Let the mixture cool to room temperature.
Add the egg yolks, one at a time, beating thoroughly after each addition.
In a separate bowl, whip 1 c. of the cream until thickened. Gradually add the sugar, beating until the cream is stiff.
In another bowl, beat the egg whites and salt until they form stiff peaks. Gently fold the egg whites into the whipped cream.
Stir about one-third of the cream mixture thoroughly into the chocolate mixture blending well.
Add the remaining cream mixture over the chocolate base and gently fold them together. Gently fold in the vanilla extract.
Pour the mousse into individual dessert cups or a serving bowl and refrigerate until set, about 2 hours.
Before serving, whip the remaining cup of cream until thickened. Add vanilla and whip to soft peaks. Top each portion of mousse with a dollop of whipped cream.