Separate the Eggs: Separate the egg whites from the yolks, placing the whites in one mixing bowl and the yolks in another.
Whip the Egg Whites: Using an electric mixer, beat the egg whites until they become very fluffy.
Add the Sugar: Continue beating the egg whites while gradually adding the 7 tablespoons of white sugar one spoonful at a time. Set the whipped mixture aside.
Sift the Dry Ingredients: Sift the flour, cornstarch, baking powder, and baking soda together to evenly combine the dry ingredients.
Mix the Egg Yolks: Beat the egg yolks with the vanilla extract until combined, then gently add the sifted dry ingredients while mixing on low speed.
Combine the Mixtures: Fold the egg yolk and flour mixture into the whipped egg whites until the batter is well incorporated, taking care to retain the airy texture.
Prepare the Pan: Line a jelly roll pan with wax paper, then pour the batter into the prepared pan and spread it evenly using a spatula.
Bake the Sponge: Place the pan in a preheated 180°C oven and bake for 15 minutes, or until the cake is ready.
Prepare the Sugar-Dusted Paper: Place another sheet of wax paper on a work surface and scatter a thin, even layer of white sugar over the paper. This sugar will form the coating on the outside of the finished roll. Turn Out the Hot Cake: When the cake is baked, immediately turn it over onto the sugar-covered wax paper. Work while the cake is still hot so the wax paper underneath can be removed more easily. Spread the Margarine: Spread a generous amount of margarine evenly over the top surface of the warm cake.
Roll the Cake: Starting from the long side opposite you, roll the cake toward yourself to form the Pianono roll.
Slice the Roll: Cut the rolled cake into sections using a knife.
Cool Before Serving: Allow the sliced Pianono to cool before serving.
