Choc-orange cake with Jaffa buttercream

Place oranges in a saucepan, cover with water, and bring to the boil. Boil, topping up water if necessary, until soft (2-2½ hours). Drain in a colander, then place colander over a bowl and refrigerate to drain completely (6 hours or overnight). Discard seeds, then purée oranges in a food processor. Combine orange and lemon zest with 300gm orange purée. (Freeze remainder for another use.)

Preheat oven to 140°C. Grease a 21cm-diameter springform cake tin and line base and sides with baking paper. Combine sugar, almond meal, coconut, cocoa powder, baking powder and a pinch of salt in a large bowl. Add eggs to orange purée, whisk to combine, then add purée to dry ingredients and stir to combine. Spoon into tin and bake until cake is firm to touch and a skewer withdraws clean (45-50 minutes). Cool in tin (30 minutes), then turn out and cool completely. Transfer to a serving plate.

For chocolate buttercream, melt chocolate in a bowl over a saucepan of simmering water (don't let bowl touch water). Beat butter in an electric mixer fitted with the whisk attachment until pale and creamy. Sift sugar and cocoa together into a bowl, then with the motor running, add to butter a little at a time, beating until fluffy. Beat in chocolate, then fold in sour cream. Transfer to a piping bag fitted with a 1.3cm plain nozzle and pipe peaks onto cake. Scatter with orange peel and Jaffas to serve. Cake will keep refrigerated in an airtight container for 5 days.