Preheat your oven to 350°F (175°C) and grease an 8x8-inch baking dish with butter or non-stick spray.

Separate the egg yolks from the whites. Whisk the yolks with granulated sugar until pale and creamy (2-3 minutes). Beat the egg whites until soft peaks form (2-4 minutes).

Gradually mix the milk and melted butter into the egg yolk mixture, then add flour and vanilla extract, mixing until smooth.

Gently fold the beaten egg whites into the batter, keeping some lumps for texture.

Pour the batter into the greased baking dish and bake for 40-45 minutes or until golden brown with a slightly jiggly center.

Allow to cool to room temperature, then refrigerate for at least 2 hours before serving; cut into squares.