In a small bowl beat egg whites until stiff but not dry and set aside. In another bowl, beat the egg yolks until light. Gradually add the sugar and vanilla, and mix well. Sift together the flour, baking powder, and salt. Add the sifted flour mixture to the egg yolk mixture. Fold in the egg whites into the egg mixture and pour the batter into a 15 by 10 by 1-inch jelly roll pan lined with waxed paper. Bake for 8 to 10 minutes or until the cake is golden.
Loosen edges of cake, invert cake onto a towel dusted with confectioners' sugar. Gently peel wax paper off cake. Trim 1/4-inch of hard crust off each long side of the jelly roll cake. Begin with the narrow side and roll the cake and towel up together. Cool cake on rack, seam side down, for 10 to 15 minutes.
Once cake has cooled, gently unroll and spread cake with jam or jelly and re-roll. Sprinkle with confectioners' sugar or cover with whipped cream.