Begin by preheating the oven to a temperature of 325°F (163°C).

Utilize a light coating of non-stick baking spray on an 8x8 inch baking dish, ensuring an even distribution. Place the dish aside.

Using a clean mixing bowl, whisk the egg whites rigorously until they achieve a consistency characterized by stiff peaks. Once done, place them aside.

In a separate mixing bowl, combine the egg yolks with the sifted confectioners' sugar. Beat them together until the mixture exhibits a pale yellow hue.

Introduce the melted butter and tablespoon of purified water into the aforementioned mixture, ensuring they are integrated uniformly. This should be done over a mixing duration of approximately two minutes.

Incorporate the sifted all-purpose flour into the mixture, ensuring an even consistency and no visible lumps.

Gradually introduce the lukewarm milk and pure vanilla extract into the mixture, ensuring consistent blending to achieve a homogenous batter.

Carefully fold the previously whipped egg whites into the batter. It is advised to do this in three separate portions to ensure thorough integration without deflating the egg whites.

Pour the final batter into the prepared baking dish and position it in the preheated oven. The baking process should span 40-60 minutes, contingent upon individual oven specifications. It is advised to monitor the cake starting at the 40-minute mark. If the surface is browning prematurely, it is recommended to shield the cake with aluminum foil.

Upon completion of baking, remove the cake from the oven and allow it to cool to room temperature. Once adequately cooled, a light garnish of confectioners' sugar may be applied for presentation purposes.