Whisk eggs and sugar until pale and fluffy.Add milk, oil or butter, and vanilla extract, then mix well.In a separate bowl, sift flour, baking powder, salt, and cornstarch.Gradually combine dry ingredients with wet mixture and stir gently.Pour batter into a greased baking dish.Bake at 350°F (175°C) for 25–30 minutes until lightly golden.Cool slightly and serve warm or chilled.