Preheat the Oven: First, preheat your oven to 350°F (175°C). Grease your baking pan and set it aside. Preheating is essential to ensure even baking.

Separate the Eggs: Carefully separate the egg whites from the yolks. Place the egg whites in a clean, dry bowl, ensuring no yolk gets into the whites, as this can prevent them from whipping correctly.

Mix the Dry Ingredients: Whisk the flour and salt together in another bowl. This helps distribute the salt evenly and breaks up any clumps in the flour.

Combine Wet Ingredients: In a large mixing bowl, beat the egg yolks and sugar until light and fluffy. Add the melted butter, milk, lemon juice, and lemon zest. Mix well. The combination of lemon juice and zest gives the cake its vibrant flavor.

Incorporate Dry Ingredients: Gradually add the flour mixture to the wet ingredients until smooth. It's essential to add the flour slowly to prevent lumps.

Beat the Egg Whites: Using an electric mixer, beat the egg whites until stiff peaks form. This step is crucial for creating a light, airy texture in the cake.

Fold in the Egg Whites: Gently fold the egg whites into the batter. The batter will be thin and slightly lumpy, but that's okay. Be careful not to overmix, as this can deflate the egg whites.

Pour the Batter: Pour the batter into the prepared baking pan and spread it evenly. Ensure the batter is level enough to bake.

Bake: Place the pan in the oven and bake for 45 minutes until the top is lightly golden and the center is set. You can test for doneness by inserting a toothpick into the center of the cake; it should come out clean.

Cool the Cake: Remove the cake from the oven and let it cool completely on a cooling rack. Cooling is essential as it allows the custard layer to set correctly.