Separate the egg whites from the yolks. Whisk the yolks with the sugar and water until pale.

Add the melted butter and stir. Sift in the flour with the salt, add the vanilla, and mix well again.

Pour in the milk and stir - the batter will be thin, which is exactly right.

In a separate bowl, whip the egg whites into a stiff, fluffy foam and quickly, gently fold them into the batter.

Grease the pan with butter, pour in the batter, and bake for 50 minutes at 150°C. Do not open the oven door while baking.

Leave the finished cake in the turned-off oven for another 30 minutes, then remove and let cool. The top should have a crisp sponge crust, and the cake itself should jiggle slightly when pressed.