Preheat the oven to 160 °C (320 °F) in static mode, with top and bottom heat.

Line the bottom of the springform pan with parchment paper and grease the edges with butter.

Separate the egg whites and yolks into two different bowls.

Add half of the sugar to the bowl of egg whites. Whip the egg whites with half the sugar using an electric mixer to stiff peaks. Stop beating when the egg whites form a line, indicating they have reached stiff peaks. Set aside.

Add the remaining sugar to the bowl of yolks. Mix the mixture using the electric mixer without cleaning between uses. The yolks will lighten in color and texture, stopping when a line forms, similar to the egg whites.

Add the sifted flour to the egg yolks gradually through a strainer or sieve.

Now, use a folding motion to incorporate the mixtures gently. To maintain volume, alternate additions of 2–3 spoonfuls of egg whites and sifted flour. Carefully avoid deflating the mixture, as it does not contain leavening agents. Add more flour and when mixing becomes difficult, incorporate more egg whites. Continue folding gently until fully combined.

Pour the cake batter into the prepared springform pan. Smooth the surface with a spatula.

Place the pan on a tray on the middle rack of the preheated oven. Bake at 160 °C (320 °F) for 30–35 minutes, until lightly golden brown. The cake is done when it stops rising and begins to fall slightly. Test for doneness by inserting a skewer, which should come out clean. For this recipe, baking took 35 minutes.

Remove the cake from the oven and allow it to rest in the pan for a few minutes before inverting onto a wire rack to cool completely.

Add milk and vanilla extract to a saucepan.

Heat the milk over low heat.

In a separate bowl, whisk together egg yolks, sugar, and sifted corn starch until well combined.

Slowly pour the heated milk into the egg yolk mixture while whisking constantly.

Pour the mixture back into the saucepan and return it to low heat. Continue stirring continuously until the pastry cream thickens to a coating consistency.

Remove the pastry cream from the heat and immediately pour it into a bowl to cool completely.

Whip heavy cream with sifted powdered sugar until full volume is reached and soft peaks form.

Once cooled, gently fold the whipped cream into the pastry cream using a spatula, mixing from the bottom but being careful not to overmix.

To prepare the syrup, bring the water and sugar to a boil while stirring continuously.

Once the sugar has completely dissolved, add the lemon juice and continue cooking briefly while maintaining the boil.

Then remove from the heat and allow it to fully cool at room temperature before use or storage.

Carefully cut the sponge cake into 3 even rounds, aiming for uniform thickness across all discs.

Gently scrape any browned portions of the first disc using a small knife. Remove all darkened areas to reveal the pristine yellow base free of burns or imperfections.

Cut the disc into small pieces approximately 1 centimeter wide or slightly smaller.

Place the first round on the tray and moisten the top lightly with syrup from the outer edge inward.

Spread an even layer of diplomatic cream over, leveling it smooth.

Top with the second round, moistening the top.

Finish by spreading the remaining diplomatic cream in an even layer across the entire structure, leveling and feathering the cream up along the outer edge.

Place any remaining sponge cake pieces on and around the cake to resemble a mimosa flower. Gently press pieces into place.

Refrigerate the completed traditional mimosa cake for approximately 2 hours before serving.