Instructions.
To make the sponge cake:
1. To begin, lightly butter the cake tin and line the bottom with baking parchment.
2. Combine the eggs and sugar in a large bowl and stir well until the cake mixture is pale and thick.
3. Sift in the flour and cocoa powder over the top of the bowl using a sieve. Fold in the flour and cocoa until the cake mixture is fully incorporated.
4. Pour the cake batter into the prepared cake tin and bake in the oven at 180C (160C for fan or Gas 4) for 45 minutes or until the sponge has risen.
5. When fully cooked, take the sponge cake out of the oven, take it out of the cake tin, and leave it on a wire rack to cool.
6. Once fully cooled, cut the cake in half horizontally and place one half back onto a clean cake tin.
To make the mousse:
7. Break the chocolate into chunks then place them into a heatproof bowl. Set the bowl over a pan of hot water and gently melt the chocolate. Stir it occasionally and wait for it to fully melt, then set aside to cool.
8. Strain the orange juice into a small heatproof bowl and sprinkle it over the gelatine. Leave it for three minutes until it is spongy, then set the bowl over a saucepan of gently simmering water for three minutes until the gelatine has dissolved.
9. Stir in the egg yolk and orange zest into the cooled-down chocolate. Slowly stir in the dissolved gelatine, then fold in the whipping cream.
10. In a separate bowl, whisk the egg whites until they are stiff and not dry, then gently fold them into the chocolate mousse mixture until fully incorporated.
Mary Berry warned: “When making the mousse, do not over-whisk the egg whites, when they just flop over at the tip they are ready to fold into the chocolate mixture.”
Assemble it all together:
11. Pour the chocolate mousse mixture on top of the cake layer sitting in the tin, then place the remaining cake layer on top.
12. Place the cake in the fridge and leave the cake until the mousse has fully set.
13. Once set, remove the cake tin and slide the cake serving plate. To decorate, cover the top of the cake with a layer of cream then decorate with orange zest.
14. Your delicious orange and chocolate mousse cake is now ready to serve.
