Beat the egg yolks and 50 grams of sugar until pale in color followed by the water, vegetable oil, vanilla extract and cake flour. Beat for 5 to 8 minutes. Set aside.
Make a meringue by beating the egg whites and the remaining 50 grams of sugar. Add the sugar in 3 parts.
Fold in the meringue to the egg yolk mixture. Color if desired.
Place half of the batter in a piping bag and pipe over your drawing batter making sure all the gaps are filled. Pour the rest of the batter and level the top of it. Tap the pan to release air bubbles.
Place in a pre-heated oven of 170 degrees Celsius and bake for 15 minutes.