Break up the chocolate into small cubes. Gently melt the chocolate in a saucepan on a low heat. Add the milk and butter, stirring continuously until the chocolate is melted.
While the chocolate is melting, line a baking tine with baking paper and set aside.
Remove from the heat and pour in the Irish cream liqueur. Combine the mixture together well.
Pour into the baking tray and place in the oven for 4 hours or until it is set.
Remove and cut into squares.
Remove saucepan from heat and whisk in Irish cream liqueur. Pour into slice tin and refrigerate for 3-4 hours or until set. Cut into squares.