This zingy Jaffa Cake traybake is made up of a super light base of vanilla sponge, an sweet and citrusy orange jelly layer, and an indulgent topping of dark chocolate to finish.
Take a piece of baking paper and draw a 20cm (8inch) square onto it using a ruler for accuracy. Flip the paper over (so that you don't get pencil marks on the sponge) and place on a baking tray.
Line an 18cm (7inch) square tin with a double layer of cling film.
Preheat the oven to 200C (180C fan / 390F).
Put the eggs and caster sugar in a large bowl. Using electric beaters, whisk them together until thick, pale and creamy. This will take about 5 minutes with electric beaters.
Add the vanilla, then sift the flour on top. Using a silicone spatula or large metal spoon, fold the flour into the egg mixture.
Immediately pour the sponge mix onto the lined baking sheet and gently spread to cover the square you drew.
Bake for 8 minutes until risen, golden and just firm to the touch. Slide the paper onto a wire rack for 15 minutes to cool completely.
Once the sponge is cold, cut it out where the square guide is. If you can’t see where to cut, you can flip the paper over carefully and trim with sharp scissors before flipping back.
Fit the sponge snugly inside the base of the tin and set aside.
Make the jelly
Measure 150ml (¼ pt) of steam hot (but not boiling) water into a large heatproof jug and sprinkle the gelatine on top. Stir gently until the gelatine dissolves.
If your jug is big enough, add the orange juice and sugar. If not, transfer everything to a bowl. Gently stir together until the sugar grains have dissolved.
Leave to cool until just on the point of setting - you should see that it is just starting to set at the sides) then pour the jelly over the sponge base.
Chill for at least 2 hours to set firmly.
Make the chocolate topping
Put the dark chocolate, milk chocolates, butter and 2 tbsp water in a bowl. Microwave for 15 seconds, stir gently then microwave for another 15 seconds, continuing until everything is just melted together. Take care not to overheat the chocolate as it may seize. Allow to cool for at least 10 minutes until it doesn’t feel warm to the touch - you don’t want to melt your jelly!
Spoon the chocolate over the set orange jelly and level off - it will set quickly as it touches the chilled jelly.
Place in the fridge for 30 minutes to firm up.
To slice and serve
To remove the cake from the tin, place a light board lined with baking paper or clingfilm on top of the tin, then invert it so that the cake drops out. Peel the clingfilm off the backing, then place another light board on top and gently invert the cake back the right way up.
Since the chocolate is firm and the jelly wobbly, this cake can be tricky to slice. To do so neatly, Sit a sharp knife in a bowl of hot water. Wipe the knife dry and score a 4x4 pattern, just cutting through the chocolate layer. Reward and wipe the knife as necessary.
Now, allowing your knife to cool, follow the scored pattern to cut through the jelly and cake layers and you’ll have beautiful little Jaffa Cake traybake bites to enjoy.