For the jelly
For the sponge
- unsalted butter, for greasing
- 1 large free-range egg
- 25g/1oz caster sugar
- 25g/1oz self-raising flour, sifted
For the topping
- 180g/6¼oz plain chocolate (about 36% cocoa solids)
For the jelly, break the jelly into pieces and place in a small bowl. Pour over the boiling water and stir until the jelly is completely dissolved. Add the orange zest, then pour into a shallow 30x20cm/12x8in tray. Chill in the fridge for 1 hour, or until set.
Meanwhile, preheat the oven to 180C/160C Fan/Gas 4 and grease a 12-hole, shallow bun tin with butter.
For the sponge, whisk the egg and sugar together for 4-5 minutes until pale and fluffy, then gently fold in the flour. Fill each well in the bun tin three-quarters full (about a dessert spoonful per hole) and smooth the tops. Bake for 7-9 minutes, or until well risen and the top of the sponges spring back when lightly pressed. Leave to cool in the tray for a few minutes then finish cooling on a wire rack.
To assemble, break the chocolate into pieces then melt in a bowl set over a pan of gently simmering water. Remove the bowl from the heat and leave to cool and thicken slightly.
Turn the jelly out onto a sheet of non-stick baking parchment. Cut 12 discs from the orange jelly using a 5cm/2in round cutter. Sit one jelly disc on top of each sponge.
Spoon the melted chocolate over the jelly discs. Using the tips of the tines of a fork or a skewer, lightly press to create a criss-cross pattern on top of the chocolate, then leave to set completely. You may need to reheat the chocolate a little if it starts to set before you have finished all the jaffa cakes.