Combine the egg yolks, salt and 50grams sugar. Whisk until light in color and has doubled in size. Set aside.
Beat the egg whites until stiff peak while adding the 70 grams sugar in 3 parts.
Fold the egg yolk mixture to the meringue until combined.
Add the sifted cake flour and baking powder to the batter, folding until all the flour is absorbed.
Combine the milk and vegetable oil in a bowl.
Put some of the batter mixture to the liquid and mix until combined then pour it back to the mixture. Fold until just incorporated.
Divide the batter into 6 bowls and color them according to your preference. Transfer them to a piping bag and pipe them to the pan with alternating colors.
Baked in the pre-heated oven for 20 minutes.