Chocolate orange cake

Preheat the oven to 180ºC/Fan 160ºF/350ºF/gas mark 4. Line a 20cm (8-inch) round cake tin with lightly oiled baking parchment paper. Place the eggs and sugar in a large bowl, over a pan of simmering water. Use an electric whisk to whisk the eggs until creamy and thick, enough to leave a trail when the whisk heads are lifted from the mixture. Sift over the flour, cocoa and baking powder and gently fold in. When the flour is almost mixed in, add the olive oil, orange zest and juice and gently fold in. Pour into the prepared tin and bake for 20-25 mins or until the cake is risen and spongy - the sponge should bounce back when lightly touched in the centre. Cool in the tin for 10 mins before transferring to a wire rack to cool. For the icing, cream the butter and icing sugar together with an electric whisk until fluffy. Add the chocolate and whisk again until smooth. Spread the icing over the top of the cold cake, then decorate with the chopped chocolate. Serve in wedges decorated with orange zest if desired.