Heat the oven to 180°C (160°C fan). Lightly grease a 12-hole bun tin (cases optional).
Whisk eggs and sugar for 4 to 5 minutes until pale, thick, and it leaves a ribbon trail.
Sift in the flour (and baking powder, if using), then fold gently until no dry flour is visible.
Spoon into the tin (about half full). Bake 8 to 10 minutes until springy and just golden. Cool on a rack.
Make up the orange jelly, then let it cool until it becomes syrupy.
Classic method: pour jelly into a shallow tray, chill until just set, then cut 12 circles to fit. Easy method: spoon semi-set jelly onto each sponge and chill.
Melt chocolate with oil or butter, then cool for 2 minutes so it’s not too hot.
Spoon a thin layer of chocolate over each cake. Chill 10 minutes, then let them sit at room temp for the best flavour.