Preheat oven to 325 F degrees.
Combine ube powder and water, set aside.
Sift four, cornstarch, baking powder and sugar in a large bowl ad make a well in the center.
Add cooking oil, egg yolks, use powder mixture and use color/flavor.
Using your mixer or wooden spoon, mix until smooth but do not over beat/mix, set aside.
Put egg whites and cream of tartar in the bowl of your mixer until frothy then gradually add sugar and beat until glossy.
Gently fold egg whites into flour mixture, taking care not to knock the air out.
Lift and fold gently until the two mixtures are well-blended.
It should have a uniform color and no white streaks remaining.
Divide and pour batter into two 6-inch baking pan and bake for about 35 minutes or until a cake tester (or toothpick) inserted comes out clean.
Transfer cakes onto a wire rack.
Let cool for about 5 minutes then run a knife around the edges and invert to cool completely before frosting.