Preheat overn to 375F. Lightly coat with Pam spray on 11X13 inch or two 9 inch layer cake. Lightly dust the pan with a little flour. Juice enough limes 1/3 cup lime about 2 limes.
In large mixing bow combine the cornstarch in the 1/3 cup lime juice using a wire whisk until slightly frothy. Add oil,water,sugar, salt and vanilla. Mix well.
In another bowl, combine the flour and baking powder.Sift well to combine. Sift the flour mixture int the bowl with cornstarch mixture. Combine thorougtly with a whisk or rubber spatula just until all is mixed well.
Pour batter into the oiled baking pan and bake for about 20 minutes or until done. Remove from the oven and let cool completely.
Serve as is, with berries and custard, or fill and frost as you wish Lime Curd or Vanilla custard make great fillings.