Preheat oven to 320ºF/160ºC.
In a large bowl, mix the egg yolks, honey, lemon zest and vanilla extract, gradually add in the vegetable oil and beat for 3 about minutes. Add in the milk.
In a separate bowl, sift the flour and the baking powder. Add to the egg mixture.
In another bowl, beat the egg whites with a pinch of salt until the peak stands straight up when the beaters are lifted from the mixture.
With a rubber spatula, gently mix about a third of the egg white mixture to the batter. Repeat the process 2 more times.
Pour the batter into prepared pans. Bake in a water bath for about 30 minutes, until a toothpick inserted in the center of the cake comes out clean.
Transfer pans to a wire rack and let cool for 10 minutes. Invert cakes onto the rack cool completely before frosting.