Light chocolate sponge, creamy buttercream with a hint of orange and a rich, chocolate ganache coating, this bake will test your rolling skills, but the chocolate-orange treat at the end will be totally worth it.
Heat the oven to 180°C/160°C fan/350°F/Gas 4.
Make the sponge. In a mixing bowl, beat together the cocoa powder, butter, orange essence, orange zest and boiling water to form a thick paste.
Whisk the egg yolks and 160g of the caster sugar in a stand mixer fitted with the whisk, on a medium–high speed for 5 minutes, until pale and thick. Add the chocolate-orange paste and mix again to combine. Transfer the mixture to a separate bowl and thoroughly clean the bowl of the stand mixer.
Whisk the egg whites in the stand mixer fitted with the whisk, on medium speed until soft peaks form. Increase the speed to high and, a spoonful at a time, add the remaining 80g of caster sugar. Continue whisking until the meringue holds stiff peaks.
Fold one quarter of the meringue mixture into the chocolate mixture to loosen, then fold in the remaining meringue until fully incorporated.
Divide the mixture equally between the prepared Swiss roll tins. Bake for 13–15 minutes, until just firm, then remove from the oven and cover with a clean tea towel. Leave to cool completely.
Meanwhile, make the filling. Beat together the butter and vegetable shortening in a stand mixer fitted with the beater until pale and creamy. Gradually add the icing sugar and continue beating until fluffy. Add the orange essence and enough milk to achieve a smooth, spreadable consistency, then mix to combine.
Make the chocolate ganache. Tip the chocolate into a heatproof bowl. Pour the cream into a small saucepan and place it over a medium heat. Bring to the boil, then immediately pour the hot cream over the chocolate. Leave for 2 minutes to melt the chocolate, then stir until smooth. Set aside.
Turn out the cooled sponges onto a piece of baking paper. Score a line across the sponges3cm in from each of the short edges. Divide the buttercream equally between the sponges and spread it out evenly(it doesn’t matter if you spread over your score line).
Turn one of the sponges so that you have a short edge closest to you. Starting at the nearest short edge, firmly roll into the middle of the sheet of sponge. Stop, then turn the sponge through 180° and repeat, rolling up from the opposite short edge, so that the rolls meet in the middle, like a scroll. Cut down the middle, between the rolls, to separate in two. Repeat with the second sponge, so you have four rolls altogether.
Trim the ends of the rolls and cut each roll into 3 equal pieces along its length, to give you 12 individual mini rolls.
Place the mini rolls, seam-sides downwards on a wire rack with a baking tray underneath(to catch the drips). Pour the cooled ganache over each roll, ensuring you cover all sides evenly. Leave to set(cover and reserve the remaining ganache).
Heat the oven to 110°C/90°C fan/230°F/Gas ¼. Arrange the halved orange slices on the prepared tray and bake them for 1–2 hours, until completely dried. Check on the orange regularly to make sure it isn’t browning too quickly. If your oven allows it, turn the temperature down even lower or turn the oven off and allow the orange wedges to continue drying in the cooling oven. When they are crisp and dry, remove from the tray and set aside to cool.
To decorate, transfer the rolls to a serving platter. Use a little of the leftover ganache to stick an orange slice to the top of each mini roll. Finish with a few flakes of gold leaf, if using.