This is a chocoholics dream. The rich, dark chocolate mousse hides a coffee-mousse centre all robed in a chocolate mirror glaze and served with almond brittle.
For the chocolate mousse, put the egg yolks, egg and caster sugar in the bowl of a stand mixer. Place the bowl over a pan of gently simmering water and stir until the mixture reaches 60°C/140°F on the cooking thermometer. Remove from the heat, place the bowl back on the mixer (fitted with the whisk) and whisk on medium–high speed for 3–4 minutes, until the bowl is cool to the touch and the mixture is thick and leaves a ribbon trail when the whisk is lifted.
In a separate bowl, use a hand-held electric whisk to whisk the double cream to soft peaks. Set aside.
Place the whipping cream in a small pan over a medium heat and bring just up to the boil. Remove from the heat, add the chocolate, leave for 3 minutes, then stir until smooth. Add a heaped spoonful of the whisked cream to the chocolate mixture, then fold the chocolate mixture and the remaining whisked cream into the egg and sugar mixture, until no streaks remain. Pour into the lined glass bowl and place in the freezer to set for about 2½ hours (but don’t let it freeze completely).
For the coffee crème anglaise, place the gelatine in a bowl with 4 tablespoons of water. Place 15g of the caster sugar and the egg yolks into a small bowl and mix with a wooden spoon until combined.
Pour the milk, 50ml of the cream and the coffee extract into a small pan set over a low heat. Heat to just below boiling point, then pour in a thin stream onto the egg-yolk mixture, stirring continuously. Return the mixture to the pan and heat slowly, stirring continuously, for 2–3 minutes, until it reaches 82°C/180°F on the thermometer and just coats the back of spoon. Remove from the heat and pour through a sieve into a medium bowl. Remove the gelatine from the water, shaking off the excess, and stir into the crème anglaise.
Pour the remaining double cream and a further 15g of caster sugar into a medium bowl and use a hand-held electric whisk to whip to soft peaks.
Place the egg whites and remaining 25g of caster sugar into the bowl of stand mixer. Place over a pan of gently simmering water and stir gently until the mixture reaches 60°C/140°F on the thermometer. Put the bowl back on the mixer (fitted with the whisk) and whisk to soft peaks.
Fold the whipped, sweetened cream into the coffee crème anglaise, then fold in the egg whites until combined. Pour into a small bowl and place in the freezer.
To make the joconde sponge, heat the oven to 220°C/200°C fan/425°F/Gas 7. Whisk the egg whites in the clean bowl of a stand mixer until they form firm peaks. Gradually add the caster sugar and whisk until smooth and glossy. Transfer the mixture to another large bowl and set aside covered in cling film.
Place the ground almonds, icing sugar and eggs in the bowl of the mixer and whisk for about 5 minutes until doubled in volume. Fold in the flour and melted butter, then gently fold in the whisked egg whites.
Pour the mixture onto the lined baking tray and smooth it out with a palette knife. Bake for 7–10 minutes, until pale golden and firm. Dust with caster sugar, then turn out onto the lined wire rack. Remove the uppermost baking paper and leave the joconde to cool. Using the paper template, cut out a 21cm-diameter circle from the cooled sponge.
For the syrup, heat the sugar and 50ml of water in a small pan over a medium heat until the sugar has dissolved. Bring to the boil and simmer for 2 minutes, then stir in the almond liqueur. Set aside.
For the brittle, place the sugar in a medium pan over a medium heat. Heat, shaking the pan (but not stirring) until the mixture turns a dark amber colour. Then, stir in the butter and almonds. Pour onto the silicone mat and leave to set. Once set, break up into small pieces and set aside until you’re ready to decorate.
Once the chocolate mousse and coffee crème anglaise have set (but are not frozen), scoop out some of the chocolate mousse from the centre of the bowl, and fill with the coffee crème anglaise. (See tip for how to use any leftovers.)
Brush the circle of joconde sponge with almond liqueur syrup and place on top of the mousse. Place in the fridge to set for at least 4 hours or overnight.
Set the cake board on a plate and, using the cling film, ease the bombe out of the bowl, placing it on the board. Use a spatula dipped in some warm water to smooth over the mousse and remove any crease marks to give an even surface. Return to the fridge for a further 10 minutes.
For the mirror glaze, put the cream, sugar and cocoa in a small pan with 150ml of water. Dissolve the sugar and cocoa in the cream over a low heat, then increase the heat so that the mixture comes to the boil. Simmer for 2 minutes. Remove from the heat and set aside to cool for about 10 minutes.
While the cream mixture is cooling, soak the gelatine in water for 5 minutes. Drain, then stir into the cream mixture to fully incorporate. Pass the mixture through a sieve into a bowl, then place in the fridge to cool to 20°C/68°F on the cooking thermometer, or until thick enough to coat the back of a spoon.
Place the bombe on a wire rack set over a sheet of baking paper to catch the drips. Pour the mirror glaze evenly all over the dome, then chill for 15 minutes to set.
To decorate, melt the white chocolate in a small bowl set over a pan of gently simmering water. Transfer to the piping bag.
Remove the bombe from the fridge, snip the end of the piping bag and drizzle the white chocolate over. Arrange the broken almond brittle around the bottom of the bombe to serve.
Tip: You will have a little sponge and some of the chocolate mousse and the coffee crème left over. Cut the sponge into small circles, place in the base of individual dessert glasses and top with the leftover mousse and coffee crème, then chill.