Start by making the jelly. Line a 20cm/8in square cake tin with baking parchment. Place the agar agar powder in a saucepan and gradually whisk in the orange juice, making sure that there are no lumps.
Whisk in the lemon juice and sugar then bring the mixture to a boil. Boil for 1 minute, stirring constantly. Pour the jelly into the tin and refrigerate until set (about 1 hour).
Preheat the oven to 180°C/160°C fan/350°F/gas mark 4. Grease a 12 hole bun or muffin tin.
Sift together the plain flour, cornflour and baking powder into a bowl. Add the sugar, milk, oil and orange extract and whisk with a balloon whisk until smooth.
Divide the batter between the tin, about 1 Tablespoon of batter per hole. Bash the tin on the counter to burst any air bubbles.
Bake for 12 minutes until a skewer inserted into the centre of one of the cakes comes out clean.
Let the cakes cool in the tin for 5-10 minutes then carefully turn them out onto a wire rack to cool completely.
Once the jelly is set, use a 4cm round cutter to cut out circles.
Use a sharp serrated knife to trim the tops of the cooled cakes to level them. Place a jelly circle on top of each cake.
Melt the chocolate, either in short bursts in the microwave, or in a bowl over a pan of gently simmering water (don't let the bottom of the bowl touch the water).
Use a teaspoon to spread a little melted chocolate over the top of each cake, making sure that the jelly is fully enclosed.
Use the back of a fork to gently make an indentation in the top of the chocolate (optional, purely for looks) then leave them to set before serving.