HEAT oven to 400°F. COAT 15½ x 10½ x 1-inch jelly roll pan with cooking spray. LINE bottom with waxed or parchment paper; SPRAY paper with cooking spray.
BEAT egg whites and cream of tartar in mixer bowl with whisk attachment on high speed until foamy. Beating constantly, ADD ⅓ cup of the granulated sugar, 2 Tbsp. at a time, BEATING after each addition until sugar is dissolved before adding the next. (RUB a bit of mixture between thumb and forefinger; it should feel completely smooth.) CONTINUE beating until whites are glossy and stand in soft peaks.
BEAT egg yolks in clean mixer bowl on high speed until thick and lemon-colored, 3 to 5 minutes. Gradually BEAT in remaining ⅓ cup granulated sugar until mixture is pale yellow and sugar is dissolved. BEAT in vanilla and salt.
SIFT flour over egg whites. ADD yolk mixture. FOLD gently but thoroughly until color is uniform and no streaks of flour remain. Do not stir. SPREAD into prepared pan.
BAKE in 400°F oven until center springs back when lightly tapped with finger, 10 to 12 minutes.
SPRINKLE clean kitchen towel with powdered sugar. LOOSEN cake from sides of pan with knife. INVERT cake onto towel; carefully PEEL off waxed paper. TRIM all cake edges with serrated knife. ROLL up cake, starting from short end and rolling towel in with cake. COOL wrapped cake roll, seam-side down on wire rack.
Try filling this light sponge cake roll with sliced strawberries, peaches or bananas folded into whipped cream, lemon curd or custard. Dust with powdered sugar.
To fill a cake roll, carefully unwrap cooled cake; remove towel. Spread evenly with filling re-roll cake. Refrigerate, covered and seam-side down. Sprinkle with powdered sugar before serving. Cut crosswise into slices with serrated knife.
Make ahead tip: Cooled unfilled sponge cake roll can be frozen, wrapped well in aluminum foil or plastic wrap. Defrost wrapped cake roll at room temperature, about 1 hour, before filling.
Add sugar gradually. For optimum volume and smoothest texture, sugar should be added gradually, beginning only after the egg whites or yolks have been beaten to the proper stage. Adding some or all of the sugar before beginning to beat will result in less volume.
This recipe is a good source of choline.