1/3 cup cornstarch
1/3 cup flour
5 egg yolks (1/3 cup)
1 tsp vanilla
5 egg whites
1/2 tsp. salt
1/3 cup sugar
powdered sugar
1/2 cup jelly or more to taste
whipped cream
Preheat oven to 400. Grease a 10 x 15 x 1/2 inch baking sheet and line it with parchment paper. Grease and lightly flour the paper.
Sift the cornstarch and flour. Put the egg yolks in a small bowl, add the vanilla, and stir to blend.
Beat the egg whites and salt in a large mixing bowl until foamy. Add the sugar gradually while beating, and continue to beat until the whites are stiff but moist. Fold one quarter of the beaten whites into the yolk mixture until just blended, then pour the yolk mixture over the remaining whites. Sift the flour-cornstarch mixture over the top, then fold the batter just until there are no streaks of egg white or flour showing. Spread the batter evenly in the prepared pan. Bake for 10 to 12 minutes, or until the top is light golden and a toothpick inserted in the center of the cake comes out clean.
While the cake is baking, dust a clean kitchen towel generously with powdered sugar sifted through a strainer. When the cake is done, remove from the oven and immediately turn it out onto the sugared towel. Peel off the paper. Roll the cake up in the towel from the long side and let it rest for a minute, then unroll and let rest a few minutes more. Roll back up in the towel and let it cool completely.
Unroll the cooled cake, and spread the surface with jelly (and whipped cream if desired). Re-roll the cake and place it on a serving platter, seam side down. Dust with powdered sugar.