Melt the butter, golden syrup and cocoa powder in a large saucepan over a medium heat until melted and smooth stirring occasionally.
Break the digestive biscuits up into chunks. Put the biscuit chunks and raisins in a large bowl and pour in the melted chocolate mixture.
Mix well until the biscuits and raisins are evenly dispersed.
Press this mixture into a lined baking tray, using a tablespoon to push into the tin. Cover with a sheet of greaseproof paper, then a tray covered in jam jars or tins to apply pressure on the cake and compress it even more.
Leave to cool. Once cooled, refrigerate for a couple of hours or overnight if possible.
Add marshmallows to the mix if you wish to make them more like rocky road bars.
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