Preheat the oven to 180°C / 350°F and grease the 33 × 22 cm baking pan with vegetable oil.

Dust the greased pan with a little all-purpose flour and tap out the excess.

Whisk the egg whites until foamy, then gradually beat in 8 tablespoons of granulated sugar until stiff peaks form.

Fold 8 tablespoons of all-purpose flour gently into the meringue until no dry flour remains.

Pour the batter into the prepared baking pan and level the surface.

Tap the pan several times on the counter to release air bubbles, then bake for about 15 minutes.

Mix 250 ml of warm whole milk with 3 tablespoons of granulated sugar until dissolved.

Pierce the hot sponge all over with a fork, then pour the sweetened warm milk evenly over it.

Return the sponge to the switched-off oven for a few minutes so it absorbs the milk.

Whisk the egg yolks with 8 tablespoons of granulated sugar until pale and smooth.

Whisk vanilla pudding powder, 3 tablespoons of all-purpose flour, and a small amount of the 800 ml whole milk into the yolk mixture.

Bring the remaining whole milk to a boil, then pour in the yolk mixture while whisking continuously.

Cook the custard over medium heat until thick, then remove it from the heat.

Press plastic wrap directly onto the custard surface and let it cool completely.

Beat room-temperature margarine into the cooled custard until smooth and fluffy.

Chop the strawberries, then fold them into the custard cream.

Spread the strawberry custard cream evenly over the soaked sponge.

Whip the whipping cream until firm peaks form, then spread it over the custard layer.

Chill the cake until set, then cut it into 12 cubes.