Begin by placing the gelatine powder in a small bowl and stirring in a little cold water, following the guidance from your ingredients. Leave it aside to bloom gently.

In a heatproof bowl, combine the zest of one lemon with the egg yolks and caster sugar. Mix until everything is well blended.

Warm the lemon juice in a saucepan until it just begins to simmer, then slowly pour it over the egg and sugar mixture, whisking as you go. Once combined, return everything to the saucepan.

Set the pan over medium low heat and stir continuously until the mixture thickens slightly. Take it off the heat, add the prepared gelatine, and whisk until fully dissolved. Transfer to a clean bowl, press plastic wrap directly onto the surface, and let it rest until properly chilled, about one hour.

In another bowl, whip the cream until it holds firm peaks.

Once the lemon mixture is ready, give it a light whisk to loosen if needed. Then gently fold in the whipped cream in three to four additions, working carefully to keep the mixture light and airy.

Divide the mousse into serving cups and leave it to set for at least two hours before finishing.

In a small saucepan, whisk together the lemon juice, zest, egg yolks, and sugar. Place over low heat and continue whisking for about five minutes, until it begins to thicken slightly.

Add the butter in small pieces, stirring each addition until melted before adding more. Keep cooking over low heat, whisking constantly, for 5 to 15 minutes, until the curd becomes thick and smooth.

If you wish for a perfectly silky finish, pass the curd through a fine sieve to remove any bits.

Let it sit for about 20 minutes to cool slightly, then spoon it over the set lemon mousse. Leave it to rest again until ready to serve.