Place a glass or metal bowl over a saucepan of lightly simmering water to create a bain marie. Make sure the water isn’t touching the bottom of the bowl. Drop the chopped chocolate, butter, and water into the bowl and melt together, stirring frequently with a rubber spatula.
Once the ingredients are emulsified, remove the bowl from the pan and stir in the vanilla paste. Allow the mixture to cool to room temperature.
To a separate bowl, add the cream, agave, and Bailey’s. Using a hand mixer, whip the cream to stiff peaks on a high speed. Do not over whip.
Once the chocolate mixture has cooled, add a tablespoon of the whipped cream to the chocolate and fold it together to temper. Add the remaining whipped cream and gently fold it into the chocolate mixture until no streaks of white remain.
Divide the mousse evenly between 3 serving glasses, cover with foil, and place in the fridge to set for at least 1 hour.
Serve with additional whipped cream and chocolate shavings if desired.