In a large bowl, combine egg yolks, oil, sugar, and water. Whisk until mixture is frothy and pale in color.
Add the vanilla extract or mango flavoring.
In a small bowl, combine the flour and baking powder. Add to the yolk mixture and using a hand whisk, beat the mixture until smooth. Set aside.
In the bowl of a stand mixer, beat the egg whites until frothy.
Add the cream of tartar and increase the mixer speed to medium-high. Continue to beat until the egg white form stiff peaks.
Gently fold the meringue into the yolk batter in three additions using a rubber spatula until the batter is uniform and streak-free.
Add the batter in the lightly-greased llaneras up to ¾ full.
Steam for about 15-18 minutes or until the cakes are springy to the touch and a toothpick inserted in the center of the cakes comes out clean.
Once done, turn off the heat and do NOT remove the cakes out of the steamer right away. Let rest in the steamer for about 3 minutes.
To cool, invert the laneras on top of mugs until they are cool to thetouch. To unmold the cakes, run a metal spatula or knife along the edges ofthe lanera.
Carefully remove the cakes and place them in individual container tubs ( I used 7.5 x 5 x2 inches rectangular tub).