Add chopped chocolate, butter and espresso powder to a heat-resistant bowl and place over pot of simmering water. Stir constantly until melted and smooth.
Add one yolk at a time and stir until well combined in the melted chocolate and the mixture is smooth.
In another mixing bowl, add the egg whites and 2 tablespoons sugar. Beat the egg white mixture until stiff peaks form.
In a third bowl, beat the heavy cream, Baileys Irish Cream, vanilla and sugar until it becomes the consistency of whipped cream.
Gently fold in the egg whites into the chocolate until combined. Then, fold in the Baileys whipped cream. Spoon or pipe into serving glasses and chill until set.
When you need an impressive, decadent dessert that rivals a five-star restaurant, you'll love this Baileys mousse.