Method

Step 1
To make the joconde sponge for the patterned band and base, first prepare the swiss-roll tin: cut a rectangle of baking paper to fit the base. Then, using a ruler, measure the depth of the round tin and draw 2 bands of the same width down the length of the swiss-roll tin. Draw Christmas trees along each band – you can do this free hand or draw around a cookie cutter. Place the baking paper marked side down in the swiss-roll tin.

Step 2
Make the decorative paste first as it needs plenty of time to harden before you can make the sponge itself: put the butter, flour, icing sugar and egg whites into a bowl and beat thoroughly with a wooden spoon to make a smooth, thick but pipeable paste. Transfer about 1 tablespoon into a small piping bag, then colour the rest of the mixture a vibrant green using edible food colouring and spoon into a second piping bag. Snip the ends off both bags. Pipe small dots of white paste onto the baking paper (using the drawn shapes as a guide) to resemble snowflakes between the trees, then use the green paste to pipe the trees. Freeze for 20-30 minutes until hard.

Step 3
Meanwhile, heat the oven to 200°C/180°C fan/400°F/Gas 6. To make the sponge: separate the eggs, putting 4 whites into a large bowl and 4 yolks plus one whole egg into another. Whisk the whites until they form soft peaks, then whisk in the caster sugar to make a stiff meringue. Put to one side.

Step 4
Sift the almonds, icing sugar and plain flour into the bowl with the egg yolks, then add the melted butter and beat until thick and smooth – using a wooden spoon, electric hand whisk or stand mixer fitted with a paddle attachment. Sift the cocoa into a heatproof bowl, stir in the boiling water to make a smooth paste, then add to the flour mixture and beat until thoroughly combined. Add ⅓ of the egg whites to the bowl and thoroughly stir in to soften and lighten the mixture. Fold in the remaining egg whites in 3 batches using a large metal spoon or plastic spatula.

Step 5
Divide the mixture in half and spoon one portion over the hardened decorative paste in the swiss-roll tin – use an off-set palette knife to spread evenly, making sure the corners are completely filled. Spoon the rest of the mixture into the round tin and spread evenly. Put both tins into the oven and bake for about 8 minutes for the swiss-roll tin and 12-15 minutes for the round tin, until the sponges spring back when gently pressed in the centre and begin to shrink away from the sides of the tins. Leave to cool for 1 minute then run a round-bladed knife around the inside of each tin to loosen the sponge and turn out onto a wire rack covered with a sheet of baking paper. Leave to cool completely.

Step 6
Wash and dry the round tin and line with a sheet of cling film, leaving the excess hanging over the rim. Press the cake card into the base. Trim the round sponge so it is 1cm high, then very carefully place it in the tin – if it breaks, just push the pieces together and make sure there are no gaps or holes. Carefully cut out the 2 bands of tree-patterned sponge (measuring again against the height of the round tin, and ensuring the bands include the trees) to fit tightly inside the round tin and sit 1cm above the rim. Arrange in the tin, pressing together the ends of the strips to make sure there are no gaps where they join. Chill until needed.

Step 7
Prepare the chocolate mousse by first making a Swiss meringue: put the egg white and sugar in a heatproof bowl and whisk with a wire hand whisk until just combined. Place over a pan of gently simmering water and stir gently with the whisk (just to keep the mixture moving, not to make a frothy meringue) until the mixture reaches 60°C/140°F on the cooking thermometer. Remove the bowl from the pan and stand it on a damp cloth (to prevent wobbling) then whisk with a hand-held electric whisk until the mixture stands in stiff peaks. Continue whisking until the mixture returns to room temperature then set aside on the worktop.

Step 8
Whip the cream until it stands in soft peaks, cover and chill until needed. Put the cocoa, water and rum into a small pan and place over a medium/low heat. Whisk until smooth, using a wire hand whisk. Bring to the boil then remove from the heat and add the chopped chocolate and whisk until melted and very smooth. Set aside, stirring frequently.

Step 9
Put the egg yolks into a heatproof bowl and whisk until thoroughly combined using a hand-held electric whisk. Heat the glucose syrup until boiling (the microwave is easiest for such a tiny amount) then pour onto the yolks in a thin, steady stream – whisking constantly. Continue whisking until the whisk leaves a distinct ribbon-like trail when lifted. Fold in the just-warm chocolate mixture. When thoroughly combined, fold in the whipped cream followed by the Swiss meringue. Spoon into the sponge-lined tin and spread evenly. Chill until firm.

Step 10
To make the raspberry mousse, whip the cream until it stands in soft peaks, cover and chill. Immerse the gelatine leaves in a bowl of cold water then leave to soften for about 5 minutes. Meanwhile, put the raspberries into a food processor and blitz to a thick puree. Pour into a sieve placed over a medium-sized pan and press down on the raspberries to extract as much juice as possible. Discard the seeds, then add the sugar and liqueur to the juice and place over a low heat. Stir until the sugar has completely dissolved and the mixture is very hot. Remove the pan from the heat.

Step 11
Remove the gelatine from the water, squeeze well to remove the excess water, then stir into the hot raspberry liquid. When completely melted and smooth, set aside to cool to room temperature, stirring occasionally. Then gradually fold the cooled raspberry mixture into the whipped cream and spoon into the tin on top of the set chocolate mousse. Return the tin to the fridge and chill until the raspberry mousse is set.

Step 12
To make the top layer of raspberry jelly: soak the gelatine as before. Put the raspberries, basil and sugar into a pan and place over a medium/low heat. Stir gently until the juices start to run and the sugar melts. As soon as the sugar has completely melted, bring it to the boil and simmer for a couple of minutes until the fruit is soft and pulpy.

Step 13
Remove the pan from the heat, squeeze the excess water from the gelatine and stir it into the raspberry mixture. Blitz with a stick blender then pour through a strainer into a jug (discard the seeds and any fragments of basil). Leave to cool to room temperature then carefully pour on top of the set raspberry mousse to almost fill the tin. Return to the fridge and leave to set.

Step 14
To make the chocolate decorations: carefully melt ¾ of the chocolate in a heatproof bowl placed over a pan of steaming hot water – don't let the base of the bowl touch the water. Stir gently until the chocolate reaches 45°C/113°F on the cooking thermometer. Remove the bowl from the pan, add the rest of the chocolate and stir until melted and cooled to 27°C/81°F. Then return the bowl to the heat and stir until it reaches 32°C/90°F – this process will temper the chocolate so it sets with a glossy finish.

Step 15
Place the acetate sheet or baking paper on the worktop and spread the tempered chocolate on top in an even layer about 3mm thick. Leave until 'leather firm', or almost set, then stamp out a few small Christmas trees with a cookie cutter, plus triangles or squares – these will top the entremet so you can be as creative as you choose. Leave to set then peel off carefully.

Step 16
When ready to serve, unclip the tin, peel off the cling film and place the entremet (still on its card base) on a serving platter. Decorate the top with fresh raspberries, basil leaves and chocolate shapes. Dust with icing sugar right before serving.