Martha Collison's chocolate tiffin

Grease and line a 20x20cm baking tin with baking parchment. Crush the digestive biscuits to crumbs, either using a food processor or a bowl and wooden spoon. You’re looking for a rubbly mixture with a few pea-sized pieces of biscuit remaining to give the tiffin some texture. Combine the crumbs with the cocoa powder and dried fruits – roughly chop any larger pieces of fruit so they combine well.

In a small pan, melt the butter and golden syrup together until smooth. Add a pinch of sea salt and then pour into the dry ingredients. Stir together until everything is really well mixed, tip into the lined tin and use a spatula to press the mixture firmly into an even layer. Chill for 20 minutes.

Meanwhile, melt both chocolates together in a bowl over a pan of simmering water until smooth. Pour the melted chocolate over the chilled base and tilt the tin to get an even covering, then chill for around 30-60 minutes, until firm. Slice into squares and store in an airtight container for up to 2 weeks.