First Step: Preheat and Prepare the Baking Dish. Preheat your oven to 325°F (160°C). Butter an 8″ x 8″ (20cm x 20cm) square cake pan or line it with parchment paper to prevent sticking and make removal easier.

Second Step: Whip Egg Whites. In a clean bowl, beat the egg whites using a mixer until stiff peaks form. Set aside carefully, as this airy mixture is crucial for the fluffy top layer of the custard cake.

Third Step: Prepare Egg Yolk Mixture. In a separate bowl, beat the egg yolks together with the sugar until pale yellow and creamy, approximately 1-2 minutes. This lightens the base and dissolves the sugar for smoothness.

Fourth Step: Combine Butter and Vanilla. Stir in the melted and slightly cooled unsalted butter along with the vanilla extract into the egg yolk mixture until fully incorporated, enriching the flavor and texture.

Fifth Step: Add Flour and Milk. Sift the all-purpose flour into the mixture and beat until just combined to avoid toughening the cake. Gradually pour in the lukewarm milk, mixing continuously to create a smooth, thin batter resembling pouring cream or crepe batter.

Sixth Step: Fold in Egg Whites. Gently fold the stiff egg whites into the batter in thirds using a spatula. Avoid overmixing; small lumps are acceptable and help support the fluffy top layer. This gentle folding preserves airiness crucial for the custard texture.

Seventh Step: Bake. Pour the batter gently into the prepared pan. Bake for 40 to 50 minutes, checking at 30 minutes. The cake is done when the top is golden brown and the center is just set with a slight jiggle the custard layer should remain delicate. If browning occurs too fast, cover loosely with foil and continue to bake in 10-minute intervals until fully set.

Final Step: Cool and Serve. Let the cake cool in the pan for about 10 minutes, then invert onto a wire rack to cool completely. Slowly cooling helps maintain the distinct three layers. Dust with powdered sugar and serve with fresh strawberries and whipped cream for an exquisite finish.