1. Melt chocolate, milk and sugar together in a steel bowl over a simmering pot of water (make sure bowl isn't touching water)!
2. Once all above is incorporated and smooth slowly add Guinness, folding with a spatula - don't over mix!
3. Now add in the diced cold butter and vanilla essence stirring slowly till completely smooth and all sugar is dissolved. Finish with the cream and let cool until warm.
4. Toast your marshmallow until golden brown and slide onto your cookie.
5. Add a dollop of the Guinness chocolate sauce, top with another cookie and enjoy!