Start by melting the chocolate in the microwave or on a double boiler. Once melted, mix in a teaspoon of butter. Set aside to let slightly cool.
In a stand mixer whip together the heavy cream, the Irish cream liquor and the sugar until the mixture reaches light stiff peaks.
Once done, set aside a cup of this mixture.
Gently fold together the melted chocolate and the whipped cream.
Spoon in the chocolate mixture into four cups and top up with the irish cream mixture. Sprinkle shaved chocolate on top.
Place in the fridge for at least 2 hours or overnight.
Serve cold.