Preheat the oven to 325°F (163°C). Line an 8x8-inch baking pan with parchment paper, leaving an overhang for easy removal, and lightly grease the pan.

In a clean mixing bowl, beat the egg whites using an electric mixer until stiff peaks form. Set aside.

In another large bowl, beat the egg yolks with the granulated sugar until the mixture becomes pale, creamy and slightly thick.

Add the melted butter and vanilla extract to the yolk mixture and mix until smooth.

Gradually add the flour and mix just until incorporated.

Stir in the fresh lemon juice and lemon zest to give the batter its bright citrus flavor.

Slowly pour in the lukewarm milk while mixing gently until the batter becomes smooth and very thin.

Carefully fold the beaten egg whites into the batter by hand. Do not fully mix them in; leave small visible lumps of egg whites as they help create the layered texture.

Pour the batter into the prepared baking pan and spread it evenly.

Bake for 40–60 minutes until the top becomes lightly golden and set, while the center remains slightly soft and custard-like.

If the top begins browning too quickly during baking, loosely cover the pan with foil.

Remove from the oven and allow the cake to cool completely in the pan.

Once cooled, dust generously with powdered sugar.

Lift the cake from the pan using the parchment paper and slice into bars.

Chill slightly before serving for the best creamy custard texture.