Place a medium heatproof bowl over a large saucepan of lightly simmering water. Add the chopped chocolate and stir occasionally until melted. Add the butter, one piece at a time and stir until melted before adding another. Add the salt and the Bailey’s and stir until completely incorporated. Whisk in the yolks, one at a time, making sure the first is fully blended before adding the next. Set the mixture aside.
Remove the saucepan of simmering water from the heat. Allow it to rest for a few minutes to cool. Add the egg whites to a clean heatproof bowl and set over the saucepan of hot water. Stir continuously until the egg whites are slightly warmed, about 2 - 3 minutes. Remove the bowl from the saucepan and using an electric mixer, beat the egg whites on medium speed until soft peaks form. Raise the speed to high and slowly add the sugar. Beat until soft peaks form. Add 1/4 of the beaten egg whites to the chocolate mixture and fold together until incorporated. Add the remaining egg whites and gently fold the mixture together, using a rubber spatula. Be gentle and try not to deflate the egg whites.
In a clean bowl with clean beaters or a whisk attachment, whip the cream to soft peaks. Gently fold the whipped cream into the mousse. Divide the mousse between 3-4 bowls, serving dishes or goblets. Refrigerate until cooled completely, then cover and keep refrigerated for at least 2 hours or until ready to serve. Top with sweetened whipped cream, chocolate shavings and/or fresh strawberries