1. Place the water in a small heat-proof cup; sprinkle the gelatine over top and let it soften for 5 minutes. Set the cup of gelatine into a small pan of simmering water for a few minutes and stir until the gelatine is dissolved. Remove from heat, but leave the cup of gelatine in the hot water.

2. Set a fine-mesh sieve over a medium bowl and set aside. In a medium heavy bottomed saucepan, combine the egg yolks and sugar and whisk until blended. Add the lemon juice, salt, and butter and cook over medium heat, whisking constantly, until the mixture thickens (7-10 minutes). Do not let the mixture boil.

   The lemon mixture is ready when you dip a spoon into the mixture and it leaves a light coating on the back of the spoon.

3. Remove from heat, and stir in the warm gelatine mixture. Immediately press the mixture through the sieve into the prepared bowl, pressing it through with a rubber spatula. Set aside.

4. In the bowl of an electric mixer, whip the cream at high speed until stiff peaks form. Set aside (this is best kept in the refrigerator to keep it cold).

5. Set the bowl of lemon curd into a larger bowl with ice water, careful not to splash any water into the lemon. Stir gently until the mixture becomes slightly cooler than room temperature (about 10 minutes).  Remove from the ice water and dry the base of the bowl.

6. Fold a large spoonful of whipped cream into the lemon mixture to lighten it, and then add the rest of the cream, folding it in gently until the mixture is well combined and a smooth pale yellow color.

To Assemble the Cake:

1. Prepare the cake by levelling it to a 1-inch (2.5cm) height. Place the vanilla cake round onto a large serving plate or cake board. Wrap the cake in a plastic cake collar or parchment paper*, taping it with scotch tape to secure it in place. Alternatively, you can use the rim of a springform pan.

   *Parchment paper is very difficult to secure in place, so I don't recommend this option unless you have to. To hold the parchment paper, make a small tear through the overlap at the ends of the paper where they join together, and fold it down, securing it in place with a paper clip.

2. Spoon about 1/2 of the lemon mousse on top of the cake layer, and spread to the edge of the collar. Sprinkle with fresh berries, and then top with the remaining mousse, spreading evenly. Refrigerate at least 2 hours, or until cold and set.

   Note: You can decorate the top of the cake with fresh berries and mint leaves, if desired.

3. Cut with a hot knife, wiping the blade clean after each cut. Store in the refrigerator.