Preparation Steps

• Preheat oven to 325°F (160°C). Grease a 9-inch baking dish.
• In a large bowl, whisk together egg yolks, granulated sugar, flour, melted butter, and vanilla extract until smooth.
• Gradually whisk in the milk and lemon zest (if using).
• In a separate clean bowl, beat egg whites until stiff peaks form.
• Gently fold the beaten egg whites into the yolk mixture.
• Pour the batter into the prepared baking dish.
• Bake for 45-55 minutes, or until the top is golden brown and a toothpick inserted into the center comes out clean.
• Let the cake cool completely in the dish before chilling in the refrigerator for at least 2 hours. Serve cold.