1 orange, zest finely grated
1 tbsp fine-shred orange marmalade
150g/5½oz plain flour
½ tsp baking powder
200g/7oz soft light brown sugar
175g/6oz golden caster sugar
25g/1oz cocoa powder
pinch of salt
200g/7oz dark chocolate with orange, roughly chopped
100g/3½oz dark chocolate, roughly chopped
250g/9oz dark chocolate chips
225g/8oz unsalted butter, diced, plus extra for greasing
4 medium free-range eggs