Preheat oven to 180°C conventional oven (400° Fahrenheit/Gas 6). Line a large rectangle-shape baking dish (approximately 31cm x 40cm) with baking paper. Lightly butter the baking paper with margarine or butter.
Using an electric mixer or hand beater, beat the egg whites with a pinch of salt until stiff peaks form. With the mixer (or hand beater) running, add the egg yolks, one at a time. Add the castor sugar, one tablespoon at a time, beating well after each addition.
Use a spatula to stir in the flour, one tablespoon at a time. You want to fold the mixture and see air bubbles rise to the surface of the cake mixture before adding additional tablespoons of cornflour.
Note: 00 is a powder-fine Italian type of flour. It is made from soft wheat varieties, and is frequently used in Italian desserts and pastas. 00 flour is available in most supermarkets, Italian food stores and gourmet delicatessens.
Stir in the lemon zest and vanilla bean seeds. Lastly add the sifted baking powder and stir until well combined.
Spread the rotolo (roulade) cake mixture into the prepared cake pan. Use the spatula to smooth the surface to a rectangle shape approximately 24cm X 30cm in size and 1cm thick. Bake for 10 minutes or until a skewer inserted in the centre comes out clean.
Allow to cool in the cake pan for 5 minutes. Turn rotolo onto a new sheet of baking paper. Carefully peel away baking paper lining that the rotolo was baked in and discard. Use the baking paper to roll up the sponge from short end. Place the rotolo seam side down and allow to cool, rolled up, for 10 minutes.
Unroll the sponge. Sift icing sugar (confectioners’ sugar) over the sponge. Spread nutella over the sponge, leaving a 1cm border around the edges. Use the baking paper to once again roll up rotolo from short end and enclose filling.
Place the rotolo, seam side down, on a serving plate. Dust with sifted icing sugar (confectioners’ sugar) over the top before serving – buon appetito.