**Melt the Chocolate:** In a double boiler or microwave-safe bowl, melt the chopped chocolate until smooth. Stir in the Baileys Irish Cream and let it cool slightly.
**Whip Egg Whites:** In a clean bowl, use an electric mixer to beat the egg whites until soft peaks form. Gradually add the sugar and continue beating until stiff peaks form.
**Whip Heavy Cream:** In a separate bowl, whip the heavy cream until soft peaks form. Set aside.
**Combine Egg Yolks and Chocolate:** Whisk the egg yolks into the cooled chocolate mixture until fully incorporated.
**Fold in Egg Whites:** Gently fold the beaten egg whites into the chocolate mixture in two additions, being careful not to deflate the mixture.
**Fold in Whipped Cream:** Finally, fold the whipped cream into the mousse until no streaks remain.
**Chill:** Divide the mousse into serving glasses or ramekins and refrigerate for at least 2 hours, or until set.
**Serve:** Top with whipped cream, chocolate shavings, or a dusting of cocoa powder before serving.