Beat the Eggs: In a large mixing bowl, combine the 4 eggs with a pinch of salt and 100 grams of sugar. Use an electric mixer to beat the mixture until it becomes light, fluffy, and triples in volume. This usually takes about 3-5 minutes.

Add the Flavorings: Gently fold in the egg yolk, the finely grated orange peel, and the vanillin or vanilla extract. Be careful not to deflate the batter.

Incorporate the Flour: Sift the 100 grams of flour over the egg mixture. Gently fold it in using a spatula until well combined, ensuring there are no lumps.

Pour and Bake: Pour the batter into a greased and floured baking dish or cake pan. Bake in a preheated oven at 350°F (175°C) for about 20 minutes or until a toothpick inserted into the center comes out clean.

Cool the Cake: Once baked, remove the sponge from the oven and let it cool completely on a wire rack.

Mix the Ingredients: In a saucepan, whisk together the 2 eggs, 150 grams of sugar, and 3 tablespoons of starch. Gradually add the 300 grams of milk and the orange juice, whisking continuously to avoid lumps.

Cook the Cream: Place the saucepan over medium heat and cook the mixture, stirring constantly, until it thickens into a smooth, custard-like cream. Remove from heat and stir in the 2 tablespoons of butter until melted and fully incorporated. Let the cream cool completely.

Prepare the Whipped Cream: In a chilled mixing bowl, whip the 200 grams of cold cream with 1 tablespoon of powdered sugar until soft peaks form. Be careful not to overwhip.

Layer the Cake: Once the sponge cake is cool, slice it in half horizontally to create two layers. Spread a generous layer of the cooled orange cream over the bottom layer. Place the top layer of the cake back on top.

Top with Whipped Cream: Spread or pipe the whipped cream over the top of the cake, creating an even layer.

Dust with Icing Sugar: Finally, dust the top of the cake with icing sugar for a beautiful finish.