• Measure out all the ingredients and separate the elements for each part
• Separate your egg whites and egg yolks into separate mixing bowls. Take care not to get any yolk in your egg whites. Use your largest bowl for the egg yolks as all the components will eventually be added into this one.
• Put the leaf gelatin into some water to allow it to soften. 

Blackcurrant coulis

• Make your blackcurrant coulis by blending the blackcurrants in a food processor and then sieving to remove the seeds.
• Divide the coulis into two, for the mousse and the topping

Sabayon

• Now make your sabayon from your egg yolks in the large mixing bowl.
• Heat a saucepan of water that the bowl can sit on top of without the water touching the bottom of the bowl. Bring it to a boil and then turn the heat down to low so it's steaming and barely simmering. 
• Add the sugar that is for this part of the recipe, and the water to the egg yolks and whisk together. Place the bowl on top of the saucepan of steaming hot water and continue to whisk vigorously for five minutes. 
• The sabayon will turn a pale creamy colour and then begin to thicken as it cooks. You will know it is ready when it is thick and gloopy and is also quite hot to touch. 
• Take the bowl off of the saucepan and whisk in the gelatin. Squeeze it in your hand first to wring out any excess water.
• Once it is all incorporated and dissolved, whisk in your blackcurrant coulis. This is now the base of your blackcurrant mousse. 
• Place this bowl in the fridge for 30 minutes and make your other blackcurrant mousse components. 

Biscuit base

• To make the biscuit base, melt the butter in a saucepan and put the biscuits/cookies in a bowl. Crush them to a crumb with the end of a rolling pin, add the lemon zest and then pour over the melted butter. Stir through to coat all the crumbs in the butter. 
• Pour the buttery biscuits into the cake tin and spread evenly across the base. Press them down to compress and form a solid layer. Set to one side in a cool place. 

Meringue

• Whisk your egg whites until they are white and frothy and form soft peaks, then slowly add the rest of the sugar. Once it has gone opaque and has a glossy sheen, it is ready. 

Assembling the mousse

• Lightly whip your cream, but don't let it get too stiff or it will be hard to incorporate into your mousse mixture. 
• Gently fold your whipped cream into the large bowl of blackcurrant mousse mixture.
• Now add the meringue in three stages, again gently folding it in to maintain the light and airy texture. Don't overwork it, but make sure it's all incorporated. Using a large metal spoon helps. 
• Pour the mousse mixture on top of the biscuit base and leave to set for 4-6 hours or overnight. Do not worry too much about it not being completely smooth, it will settle in the fridge, plus we are covering the top with the blackcurrant jelly layer! 

Blackcurrant jelly topping

• Finally using the last of your coulis, make the blackcurrant jelly layer for the top. 
• Put a teaspoon of powdered gelatin into two tablespoons of warm water and stir it until it has dissolved. 
• Add the gelatin mix and a heaped teaspoon of sieved icing sugar to the coulis and stir to combine. Add more sugar to taste.
• Pour over the top of the blackcurrant mousse cake and allow it to set for a few hours more. 

Serving your blackcurrant mousse cake

• Run a knife around the outside of the mousse cake to loosen it from the edge of the tin. Run the knife under hot water first to give a cleaner cut.
• Carefully remove the cake tin.
• Slice the mousse cake using a hot, sharp knife and serve.