Line a shallow 20cm square tin with baking paper. How to line a square cake tin video
Break up the biscuits with your hands, over a plate to save the crumbs.
Break the chocolate into squares and put in a bowl with the syrup and butter. Place it over a pan of simmering water, making sure the bowl doesn''t touch the water. Leave chocolate to melt, stirring occasionally.
Remove the bowl from the pan and stir in the biscuits, coconut and sultanas. Put in the tin and level off the top.
Leave until cold, then chill for at least 1 hour. Cut into 16 squares to serve.