Preparing the Sponge Cake

1. Preheat your oven to 350°F (175°C) and position a rack in the lower half of the oven.
2. Prepare an 8-inch springform pan by greasing it thoroughly, dusting with flour, and lining the bottom with parchment paper.
3. In a large bowl, combine eggs and sugar (4 large eggs and 1 cup sugar), then whisk on high speed for approximately 8 minutes until the mixture becomes extremely pale, fluffy, and tripled in volume. The batter should fall in ribbons when lifted.
4. Sift together the flour, cornstarch (or potato flour), baking powder, and salt in a separate bowl.
5. Using a spatula, gently fold the dry ingredients into the egg mixture with figure-8 motions until no flour streaks remain. Be careful not to deflate the air you’ve incorporated.
6. If using melted butter, fold it in last, adding in two portions and incorporating completely.
7. Pour the batter into your prepared pan and bake for 20-25 minutes until golden brown on top and a toothpick inserted in the center comes out clean.
8. Allow the cake to cool in the pan for 10 minutes before removing the springform collar and transferring to a wire rack to cool completely.

Making the Vanilla Pastry Cream

9. In a medium saucepan, combine milk, half the sugar, and vanilla bean paste (or extract) and heat until hot but not boiling.
10. Meanwhile, in a separate bowl, whisk together egg yolks, remaining sugar, and cornstarch until smooth.
11. Slowly pour about one-third of the hot milk mixture into the egg mixture while whisking constantly to temper the eggs.
12. Return the combined mixture to the saucepan with the remaining milk and cook over medium heat, stirring constantly, until the custard thickens enough to coat the back of a spoon (about 8 minutes).
13. Remove from heat and whisk in butter and salt until fully incorporated.
14. Transfer to a bowl and place plastic wrap directly on the surface to prevent a skin from forming. Cool completely.

Assembling the Princess Cake

15. Once all components are cooled, carefully slice the sponge cake horizontally into three even layers using a serrated knife.
16. Place the bottom cake layer on your serving plate, arranging parchment strips underneath the edges to keep the plate clean.
17. Spread a thin, even layer of raspberry jam over the bottom cake layer, leaving a ½-inch border around the edge.
18. Place the second cake layer on top and spread the vanilla pastry cream evenly over it, again leaving a small border.
19. Whip the heavy cream with powdered sugar and vanilla until soft peaks form – be careful not to overwhip.
20. Place the final cake layer on top, positioning it cut-side down for a smooth surface.
21. Use the whipped cream to create a dome shape, applying it generously over and around the entire cake.
22. Smooth the cream with an offset spatula, ensuring an even, rounded dome shape.
23. Refrigerate the cake for at least 30 minutes to set the cream before applying the marzipan.