I use 2 12-hole cupcake trays - one for the jelly, the other for the cake bases.
Make the Jelly
We want our jelly to be a bit firmer set and much more intensely flavoured than what comes out of the packet. So juice the orange and scrape off about a teaspoon of zest. Follow the instructions on the pack to make up the jelly, but only use half the amount of liquid (and this will include the orange juice and the zest). Take one of the cupcake trays and pour a little jelly in the bottom of each one. You will only use a small fraction of the made-up jelly, so set the rest of it in bowls. If you don't have a suitable cupcake tray, line a flat baking sheet with plastic film and pour a thin layer of jelly into this. Once the jelly is set, you can cut discs out using a small cookie cutter.
Make the Sponge Bases
First of all, grease the cupcake bumps with butter and pop it in the fridge to set (this will provide lubrication without being absorbed into the sponge when it's baking). Heat your oven to 180°C (356°F) for a fan/convection oven, 200°C (392°F) for a conventional one, gas 6.
Sift the sugar into a bowl and whisk it together with the eggs for 5-8 minutes. You want the mixture to turn pale and thicken up a bit. Technically, you need it to reach the 'ribbon' stage, which means that when you take some of the mixture out of the bowl and let it run back in, it leaves a ribbon-like trail and is not re-absorbed immediately. Fold in the flour, being careful not to knock the air out of the egg/sugar mixture. Melt the butter and add it with the almond extract. Spoon the mixture into the tin, leaving some space at the top of each cake. Bake for 8 minutes. Remove from oven and cool on a wire rack.
Assemble the Jaffa Cakes
Break the chocolate up into squares, put them in a bowl and melt it. You can either do this by placing the bowl over a pan of simmering water, or by putting it in a microwave and giving it 20-second blasts, stirring in between each one, until all the chocolate is melted, probably not more than 2 minutes. You can let the chocolate cool down a bit once it's melted.
Place a disc of jelly on each cake base and spoon chocolate over it, making sure it goes right to the edge of each cake. Refrigerate until set, then use the back of a fork dipped in very hot water to melt 3/4 lines into the top of each Jaffa cake.