a little melted butter, for greasing
100g plain chocolate, broken into pieces
280g caster sugar
240ml sunflower oil
25g cocoa powder
250g plain flour
1½ tsp baking powder
orange candied peel, to decorate
Pierce the orange with a skewer (right through). Cook in boiling water for 30 minutes until soft. Whizz the whole orange in a food processor until smooth; let cool.
Preheat the oven to 180C/gas 4/fan 160C.Grease and line the base of a 23cm/9in round cake tin. Melt the chocolate in a heatproof bowl set over a pan of simmering water or in the microwave for 2 minutes on High, stirring after 1 minute. Let cool.
In a large bowl, lightly beat the eggs, sugar and oil. Gradually beat in the puréed orange, discarding any pips, then stir in the cooled melted chocolate. Sift in the cocoa, flour and baking powder. Mix well and pour into the tin. Bake in the centre of the oven for 55 minutes, or until the cake springs back when lightly pressed in the middle.