In a mixing bowl, add the vegetable oil. Sift in the cake flour and baking powder, then mix well. Add the milk and mix again until combined.

Add the egg yolks and mix well, then add the vanilla extract and mix again. Set aside.

Beat the egg whites until they form coarse bubbles. Add the lemon juice and continue beating until fine bubbles form. Gradually add the granulated sugar while beating until stiff peaks form, about 3 minutes. Set aside.

Gently fold the beaten egg whites into the flour mixture from steps 2-3, mixing gently but quickly.

Pour the batter into cups of your desired size. Bake in a convection oven at 300°F (150°C) for 25 minutes, or until a toothpick inserted comes out clean and the top is golden. Let cool slightly. Serve with tea or coffee as desired.