In a small saucepan, heat 1/4 cup Baileys and 1/4 cup heavy cream. When it starts to boil, remove from heat immediately.
Place chocolate in a bowl and pour the hot liquid on top. Let it sit for 1 minute, then stir to incorporate. Stir constantly, until smooth and glossy. Let it cool completely to room temperature. (This is your chocolate ganache).
Sprinkle gelatin over cold water.
When the chocolate ganache has cooled, pour heavy cream into a bowl.
Add chocolate ganache. Beat for 3 minutes, until stiff peaks form.
With the mixer running on slow speed, slowly add the remaining 1/2 cup Baileys.
Melt the gelatin in the microwave tor 30-45 seconds, or on a double boiler.
Add gelatin to the mousse, with the mixer running on slow speed.
Divide mixture between 6 (3 oz) cups.
Refrigerate for at least 1 hour.
Serve with chocolate shavings or whipped cream on top.