Preheat the oven to 350°F (175°C) and grease the baking dish. Separate the eggs, placing the yolks in a large mixing bowl and the whites in a smaller bowl.
Break up the yolks, then add the vanilla extract, salt, and sugar. Pour in the milk and continue mixing until everything is evenly incorporated. Add the all-purpose flour all at once. Continue mixing until the batter looks smooth and homogeneous, then set it aside.
Beat the egg whites at low speed for 45 to 60 seconds. Once small bubbles begin to form, increase the speed and continue beating for approximately 5 to 7 minutes. The egg whites are ready when they look thick and airy and visible waves begin to form across the surface.
Add the baking powder to the cake batter. Then add half of the whipped egg whites and fold slowly until partially incorporated. The mixture does not need to look completely uniform yet.
Add the remaining whipped egg whites. Fold gently by cutting through the center and turning the batter until everything is evenly combined, being careful not to deflate the egg whites.
Pour the batter into the prepared baking dish and spread it evenly. Bake for approximately 30-35 minutes, or until a toothpick inserted into the center comes out clean. Let the cake cool completely. In the meantime prepare the 3 milks mixture.
Combine the powdered milk and kola syrup, stirring until the powdered milk begins to dissolve. Add half of the condensed milk, then gradually pour in the evaporated milk while continuing to mix.
Pour the regular milk into the mixture and stir until everything is completely combined. Taste and adjust the kola syrup or powdered milk to your preference. Strain the mixture if any lumps remain.
Once the cake has cooled completely, loosen the edges with a fork. Make holes across the entire surface so the milk mixture can penetrate the sponge.
Spoon the milk mixture over the cake in stages, allowing it to absorb between additions. Refrigerate for at least 4 hours so the sponge can absorb the liquid and the flavors can concentrate. Make sure the cake is completely chilled before decorating it.