In the bowl of an electric mixer, cream together the butter and sugar until smooth. Add the salt, vanilla, and egg, and beat until well combined. Add the flour, and mix until smooth, pausing to scrape down the sides of the bowl as necessary to incorporate all of the ingredients evenly.

Spread the cake batter into the base of a lightly greased 8 or 9-inch springform pan (it won't look like much batter; about 1 cup, just enough to cover the base of the pan in a thin layer).

Bake the cake in a 350 degree F oven for 15-20 min or until a toothpick inserted into the center comes out clean. Set aside.

While the cake is baking, bring the raspberries and water to a boil. Add the sugar and lemon juice, and cook until the mixture is boiling and the berries begin to break down.

Stir in the cornstarch mixed with water, and cook until thick (about 30 seconds to 1 minute longer). Pour the hot fruit over the cake layer, and smooth the top.

Cover the fruit filling with a layer of plastic wrap set directly on top (to prevent a "skin" from forming). Refrigerate until cold (about 2 hours).

In a heat-proof mug, sprinkle the gelatine over 3 Tbsp of cold water. Set the cup into a pan of simmering water, and stir until the gelatine is dissolved and the mixture is clear. Remove the cup from the heat and set aside.

In a medium sized mixing bowl, beat the cream cheese, icing sugar and vanilla until smooth. Set aside.

In the bowl of an electric mixer (or in a medium sized bowl with a hand held mixer), beat the cream until soft peaks form using the whisk attachment at medium-high speed. Reduce the speed to low, and gradually add the gelatine, being careful not to scrape out whatever is left in the cup. (Soak the cup immediately following this step for easy cleaning).

Increase the speed to high, and beat until the cream forms stiff peaks. Divide the cream in half, and fold it into the cream cheese mixture until smooth.

Remove the plastic wrap from the chilled raspberry cake layer, and spread the cream cheese mousse evenly over top.

Divide the remaining cream in half, and place half of the cream into a large piping bag fitted with a star tip.

Scrape the remaining cream on top of the mousse layer, and spread it into a smooth, flat layer.

Pipe rosettes around the perimeter of the cake, and decorate with fresh raspberries. Refrigerate until cold and set, at least 4 hours (but ideally overnight).

To serve the cake, set the cake onto a large serving platter, and run a thin bladed knife around the edge of the pan. Release the collar and cut the cake into slices with a long, sharp knife. Serve cold.

For a more clean look, you can warm the blade of the knife by running it under hot water, and wiping it dry before each slice you make.