Prepare the Ingredients:

1. Preheat the Oven: Preheat your oven to 325°F (165°C). Grease a 9-inch round cake pan and line the bottom with parchment paper for easy removal.
2. Separate the Eggs: Carefully separate the egg yolks from the whites. Place the egg whites in a large bowl and the yolks in another bowl.

Make the Custard and Cake Mixture:

3. Mix the Egg Yolks and Sugar: In the bowl with the egg yolks, whisk together the granulated sugar, lemon zest, lemon juice, melted butter, milk, vanilla extract, and a pinch of salt until well combined.
4. Add the Flour: Gradually add the flour to the egg yolk mixture and whisk until smooth. The mixture will be thin, which is perfect for creating the custard layer.

Whip the Egg Whites:

5. Whip the Egg Whites: Using an electric mixer, beat the egg whites in a clean bowl until stiff peaks form.
6. Fold the Egg Whites: Gently fold the whipped egg whites into the egg yolk mixture, being careful not to deflate the air you’ve incorporated. The batter will be slightly lumpy due to the whipped egg whites.

Bake the Cake:

7. Pour the Batter into the Pan: Pour the batter into the prepared cake pan and spread it evenly.
8. Bake: Bake the cake in the preheated oven for 45-55 minutes, or until the top is golden and a toothpick inserted in the center comes out clean. The custard layer will form at the bottom while the cake rises on top.
9. Cool: Let the cake cool in the pan for about 10 minutes, then run a knife around the edges to loosen it. Invert the cake onto a plate and carefully remove the parchment paper.

Serve:

10. Dust with Powdered Sugar: Once the cake has cooled, dust it with powdered sugar for a pretty presentation. Slice and serve!