Place the chopped chocolate in a large bowl. Set aside.
In a large bowl beat the egg yolks and granulated sugar with hand mixer on medium-high speed until the mixture is thick and smooth.
In a medium saucepan warm 1 cup of cream over medium-heat until it simmers.
Remove the pan from heat and slowly whisk half of the hot cream (1/2 cup) into the egg yolk/sugar mixture, whisking constantly and adding it very gradually, to temper the mixture. Slowly add another 1/4 cup of hot cream. Leave remaining cream in pan.
Transfer the mixture back to the saucepan and cook over medium-heat, stirring constantly, (until mixture is thick enough to easily coat the back of a spoon), about 5minutes.
Add the warm mixture over chopped chocolate. Stir until the chocolate is smooth and melted, then whisk in the vanilla, espresso powder, and salt. Cover and chill for 1-2hrs.
Once chilled, beat the remaining 3/4 cups of heavy cream until stiff peaks form.
Gently fold the whipped cream into the chocolate mixture, until evenly combined.
Spoon the mousse into dessert cups, top with whipped topping and chocolate shavings and enjoy