Blitz the bourbons into fine crumbs using a food processor or blender. Pour them into a bowl and set aside.
Melt the butter in a saucepan over low heat. Once melted, add the sugar, cocoa powder and water. Turn the heat up to medium-high and stir gently but continuously for around 5 minutes, until the sugar has dissolved.
Remove the pan from the heat and set aside to cool for about 15 minutes.
Once cooled, pour the liquid mixture into the bowl with biscuit crumbs. Mix well.
Filling
Prepare the buttercream filling by mixing the butter and icing sugar together. Use the milk as needed to loosen it to a spreadable consistency. Once smooth and fluffy, stir in the vanilla extract.
Place the biscuit mixture onto a large sheet of clingfilm on your work surface then use your hands to shape it into a rectangle.
Top with another sheet of clingfilm then use a rolling pin to roll it out to a rectangle that's roughly 10x14 inches.
Remove the top sheet of clingfilm and spread the buttercream all over the biscuit sheet, leaving a small gap around the edges.
Use the bottom piece of cling film to help you gently roll the biscuit into a log shape.
Carefully transfer the log to a large plate or cutting board and refrigerate for 3 hours.
Ganache
Once the log has been in the fridge for 2 hours, prepare your ganache. Melt the chopped chocolate and double cream over very low heat in a double boiler until smooth. Then set it aside to cool and thicken for 1 hour.
Once the ganache is thick enough to spread, take the log out of the fridge. Cut a section off the log diagonally then place it at the side, to create two 'branches'.
Cover the log with the ganache then use a fork to create wavy lines all over.
Refrigerate for 1 more hour, then dust with icing sugar and enjoy!
Video
Notes
Store in an airtight container in the fridge for up to 1 week.