300g 70% cocoa dark chocolate (divided into 200g and 100g)
Make the orange jelly: Break the jelly into pieces and put it into a small saucepan with the boiling water. Heat gently, stirring constantly, until the jelly cubes dissolve then pour it straight into the 20cm frying pan. Put that into the fridge for 2 hours, until fully set.
Make the cake: preheat the oven to 160C (140C fan). Grease the 30cm frying pan well and set to one side.
In a large mixing bowl, cream together the butter and sugar, then beat in the eggs one by one. Sieve in the flour and baking powder, and fold until just mixed through. Add 2 tablespoons of milk to loosen the batter - it should then drop easily from a spoon.
Pour the batter into the greased frying pan and cover the top loosely with foil, folding it over the edges. Put the cake into the pre-heated oven and bake for 40 minutes, then remove the foil and bake for another 5 minutes or until a skewer comes out clean. Let the cake cool in the pan for 15 minutes then turn it out - upside down - onto a wire rack to cool completely.
Assemble the cake: turn the cake the right way up. It should have risen without a peak but if the top isn’t flat, trim it with a knife to level it out. Carefully turn the orange jelly out of the pan into the middle of the cake.
Melt 200 grams of chocolate in a bain marie. Use a thermometer and take it to 45 C. Then remove it from the heat. Finely chop the remaining 100g of chocolate and stir it in. Stir constantly until the temperature reaches 27 C. It’s now ready to use.
Use a teaspoon to spoon melted chocolate neatly around the edge of the cake. If the chocolate is cool enough you should be able to spread it to the edges without it running over. Don’t add too much or it will run down the sides of the cake. Then spoon chocolate over the rest of the cake and use the back of a spoon to spread it around as neatly as possible.
Working quickly, before the chocolate starts to set, use a skewer to make marks in the top like a jaffa cake. Leave to cool for 1 hour then transfer to a serving plate. Use a hot knife to cut slices neatly through the chocolate and jelly.