2 medium oranges, well-scrubbed, finely grated zest and 2 tbsp juice only
½ orange, well-scrubbed
1 tsp baking powder
225g/8oz caster sugar
25g/1oz caster sugar
75²µ/2¾´Ç³ú cocoa powder
225g/8oz self-raising flour
300²µ/10½´Ç³ú dark chocolate (about 70% cocoa solids), broken into roughly 1cm/½in pieces (see recipe tip)
225g/8oz unsalted butter, cubed and softened, plus extra for greasing
300ml/½ pint double cream
4 large free-range eggs
2–3 tbsp semi-skimmed milk