Preheat the oven to 170°C (340°F). Separate the egg yolks from the egg whites and set them aside.
2
In a mixing bowl, combine the egg whites with 1/4 cup of sugar and beat until medium peaks form. Set aside.
3
In a separate mixing bowl, beat the softened butter, 1/3 cup of sugar, condensed milk, and vanilla extract until light and fluffy. Add the egg yolks and beat until well combined.
4
Sift the cake flour and baking powder together. Add half of the flour mixture to the batter and mix, then add the remaining flour mixture and mix until fully combined.
5
Fold in a dollop of the beaten egg whites to the batter, then fold in the remaining beaten egg whites until fully incorporated.
6
Brush a 9×5 inch loaf pan with oil and line it with parchment paper.
7
Pour the batter into the prepared pan and spread it evenly across the surface.
8
Bake in the preheated oven at 170°C (340°F) for 45 to 55 minutes until a skewer inserted in the center comes out clean.
9
Allow the cake to cool completely. Optionally, brush the top with melted butter.