Preheat your oven to 350°F (175°C) and grease an 8-inch round springform pan, lining the bottom with parchment paper. In a large heatproof bowl set over a pot of simmering water, combine the eggs and granulated sugar, whisking constantly until the mixture is lukewarm to the touch.

Remove the bowl from the heat and beat the egg mixture with an electric mixer on high speed for about 8 to 10 minutes. The mixture should become thick, pale yellow, and triple in volume, leaving a trail that holds its shape for a few seconds when the beaters are lifted.

Sift the all-purpose flour, cornstarch, and pinch of salt directly over the whipped egg mixture. Gently fold the dry ingredients and vanilla extract into the eggs using a rubber spatula, being careful not to deflate the airy batter.

Pour the batter into the prepared springform pan and bake for 20 to 25 minutes, or until the sponge cake is golden brown and a toothpick inserted into the center comes out clean. Allow the cake to cool in the pan for 10 minutes, then transfer it to a wire rack to cool completely.

While the cake cools, whip the cold heavy cream and powdered sugar in a chilled bowl until stiff peaks form. Be careful not to over-whip, or the cream will become grainy and buttery.

Once the sponge cake is completely cool, slice it horizontally into two equal layers using a sharp serrated knife. Place the bottom layer on a serving platter and spread the strawberry jam evenly across the top.

Spread about one-third of the whipped cream over the jam layer, then place the second cake layer gently on top. Use a spatula to frost the top and sides of the entire cake with the remaining whipped cream, reserving a small amount in a piping bag for decoration.

Gently press the toasted sliced almonds onto the sides of the cake until they are evenly coated. Pipe decorative swirls of the reserved whipped cream on top, and garnish with the fresh strawberries, kiwi, and mandarin oranges before chilling for at least 1 hour before serving.