Make the sponge cake

• Whisk the eggs with the sugar and vanilla until pale and tripled in volume.
• Fold in the sifted flour gently with a spatula.
• Pour into a lined springform pan and bake at 180 °C.

Prepare the syrup

• Bring the sugar, water and strawberry juice to a boil in a saucepan.
• Remove from the heat and let cool completely.

Make the crème mousseline

• Whisk the egg yolks with the sugar, vanilla and cornstarch.
• Heat the milk and pour it over the yolk mixture, whisking constantly.
• Return to the pan and cook, stirring, until thickened.

Enrich the cream

• Let the pastry cream cool to room temperature.
• Beat in the soft butter until smooth and airy.

Assemble the fraisier

• Line the pan with halved strawberries against the sides.
• Brush the sponge with syrup and place a layer in the pan.
• Fill with crème mousseline and diced strawberries, then top with a second sponge layer.

Chill and serve

• Refrigerate until the cream is fully set.
• Unmold and decorate with fresh strawberries.