In a large mixing bowl, sprinkle the gelatin over the water and set aside.

In a medium mixing bowl, whisk the egg yolks and cornstarch until combined.

In a medium saucepan, combine the fruit, sugar, butter, and salt. Mash and mix before turning on the heat. Cook over medium heat until the mixture is simmering and the fruit is almost completely broken down - about 4 to 6 minutes.

Temper the eggs by slowly streaming about half of the fruit into the egg yolk mixture. Whisk constantly and then return it back to the saucepan. Cook until the curd thickens and bubbles - about 1 minute.

Strain the curd through a fine-mesh strainer set over the bowl with the gelatin. Stir until the gelatin is dissolved.

Set aside, stirring occasionally, until the curd is lightly thickened and cooled to room temperature - at least 30 minutes.

Adjust oven rack to middle position and preheat the oven to 350F degrees. Line the bottom of 2, 8-inch round cake pans with parchment paper.

On a piece of wax or parchment paper, sift the cake flour and salt.

In a medium microwave-safe bowl, melt the butter. Set aside.

In a stand mixer bowl, add the eggs and sugar. Mix on low to break up the eggs, then increase speed to medium until airy and pale - about 4 to 5 minutes.

Remove from mixer and gently fold in the sifted flour in three additions.

Temper the butter by folding about 1 cup of the cake batter into the melted butter, then combine it back into the mixing bowl.

Pour the batter equally into the prepared cake pans and bake for 25 to 27 minutes or until a toothpick inserted comes out clean.

Cool the cakes in the pans for 10 minutes, then invert to cool completely.

While the cakes are cooling, finish the mousse by whipping the heavy cream until soft peaks form.

Transfer ⅓ of the whipped cream to the fruit curd. Fold in the remaining whipped cream.

Add the jam and lemon juice to a microwave-safe dish and heat until the jam is fluid.

Set one cake on a serving platter, spread half of the jam and half of the berry mousse on top. Repeat with the second cake.

Refrigerate the cake for at least 4 hours before serving.