A great centrepiece for a Christmas table. The sponge is made with cocoa and brushed with kirsch syrup then filled with chocolate mousse and kirsch-soaked black cherries. While chocolate-dipped cherries, chocolate cherry truffles and meringue mushrooms decorate the ganache-covered log.
Start by making the sponge: heat the oven to 180°C/160°C fan/350°F/Gas 4. Melt the butter and leave to cool until needed. Sift the flour, cocoa and salt onto a sheet of baking paper or into a bowl and set to one side. Immerse the eggs in a bowl of very warm water (bath-water temperature) for 5 minutes, then crack into the bowl of a stand mixer. Add the sugar and vanilla and whisk on full speed for about 5 minutes until the mixture is very thick, pale and mousse-like – the whisk should leave a distinct ribbon-like trail when lifted from the bowl.
Sift ⅓ of the (sifted) flour mixture into the bowl and very gently fold in with a large metal spoon or plastic spatula. Repeat twice more, then stir a spoonful of the mixture into the melted butter. When well combined, return the butter mixture to the bowl and gently but thoroughly fold in. Pour the mixture into the prepared swiss-roll tin and gently spread to make an even layer, making sure the corners are well filled.
Bake in the oven for about 10 minutes, until the sponge just springs back when gently pressed in the middle. Keep an eye on the sponge while it bakes as it quickly dries out – making it difficult to roll easily. Remove the tin from the oven and run a round-bladed knife around the inside of the tin to loosen the sponge. Leave to firm up for 2 minutes.
Meanwhile, place a large sheet of baking paper on top of a wire cooling rack and sprinkle lightly with caster sugar. Flip the sponge onto the paper, lift off the tin and peel away the lining paper. Make a deep cut along one long edge (about 1cm in) and firmly roll up the log from this edge – using the baking paper to help you shape the roll into a neat, tight column. Leave the paper around the roll to maintain its shape, and set aside to cool on the wire rack.
Meanwhile, make the meringue mushrooms: reduce the oven temperature to 110°C/90°C fan/225°F/Gas ½. Whisk the egg white with the cream of tartar until the mixture stands in soft peaks, then whisk in the sugar a tablespoon at a time to make a stiff, glossy meringue. Transfer to a large piping bag fitted with a 1.5cm plain nozzle and pipe 8 mounds (5cm across) on the lined baking sheet – these will be the mushroom caps. Dip your finger in cold water and gently flatten any peaks. Then pipe 8 cones (about 2cm high) for the mushroom stems. Bake in the oven for 70 minutes then turn off the oven (without opening the door) and leave the meringues to cool in the cooling oven.
Now make the ganache, which will be used to cover the log as well as make the chocolate mousse filling: put the chopped chocolate into a large, heatproof bowl. Heat the cream until steaming hot then pour over the chocolate. Leave to stand for 2 minutes then gently stir until melted and smooth. Drain the cherries from the jar into a sieve placed over a jug or bowl (to catch the syrup). Add a tablespoon of this syrup to the ganache and whisk well with a wire hand whisk for 2 minutes until lighter in texture and colour.
Working quickly, before the ganache starts to firm up, gently unroll the sponge column and lightly brush with 3 tablespoons of the cherry syrup. Next, make the filling: whip the double cream until it stands in soft peaks then fold in 100g of the ganache and 1 tablespoon of the cherry syrup. Spread over the sponge – leaving a 1cm border of sponge along the 2 short sides and the long edge without the cut. Scatter the drained cherries evenly over the filling then roll up the sponge again starting from the edge with the cut. Trim the ends of the log with a sharp, serrated knife.
Give the ganache a whisk to make sure it is smooth and spreadable, then spread thickly over the sides and ends of the log. Transfer the log to a serving board or platter and decorate with bark-like markings, using a round-bladed knife or palette knife. Mark the ends with concentric circles or swirls (like the cross-section of a tree) using the tip of a skewer. Leave to set.
To make the truffles: put the chocolate into a heatproof bowl, heat the cream until steaming hot, then pour over the chocolate. Leave to melt for a couple of minutes then stir until very smooth. Add the vanilla and liquor and beat well until thoroughly combined, then mix in the chopped cherries. Cover the bowl and chill until very firm.
Sift the cocoa onto a large plate, then take a teaspoon of the truffle mixture and roll it into a ball with your hands – aim to make truffles the same size as the fresh cherries that will go on top of the log. Quickly roll the truffle in the cocoa powder then place on a sheet of baking paper. Repeat until you have 16–18 truffles. If necessary, return the truffles to the fridge to firm up. Arrange on either side of the log and finish with gold leaf (if using).
To make the chocolate-dipped cherries: wipe the cherries with kitchen paper to make sure they are clean and dry. Place the chocolate in a small heatproof/microwave-safe bowl and melt in the microwave in 10-second bursts, then stir well until very smooth. One at a time, dip the cherries into the chocolate (holding them by their stalks) then leave to set on a strip of acetate or baking paper.
Transfer the remaining melted chocolate to a small piping bag and snip off the tip to make a fine writing tip. Pipe 4 holly-leaf shapes on the acetate or baking paper and leave to set. Attach the mushroom caps to the stalks with small dabs of melted chocolate.
To finish the yule log: carefully peel the dipped cherries and holly leaves off the acetate or baking paper and arrange on top of the log. Place the meringue mushrooms at each end and cut the log into slices with a sharp knife dipped into hot water (then wiped dry).