Break the jelly into pieces and place in a small heatproof bowl, pour over the boiling water and stir until the jelly has completely melted; stir in the orange zest; pour into a shallow tin measuring 30cm x 20cm and chill for about 1 hour until set
Heat the oven to 180C/Gas 4; to make the sponge, whisk the eggs and sugar together for 4-5 minutes until pale and fluffy then fold in the flour gently but thoroughly
Spoon the sponge mixture into a twelve-hole bun tin, greased with butter; bake for 7-9 minutes until the sponges are light, golden and puffy and they feel springy to the touch; remove from the oven and leave to cool for a few minutes before transferring to a wire rack to finish cooling
To assemble, melt the chocolate and stir until smooth, then leave to cool and thicken slightly
Cut 12 discs x 5cm from the set jelly and place a disc on each sponge
Spoon the melted chocolate over the jelly discs; allow to set slightly, then use a fork to create a criss-cross pattern on top of the chocolate; leave to set completely before serving
12 servings