Separate eggs, keeping yolks and whites; let stand at room temperature 1 hour.
Heat oven to 350 degrees F. Lightly coat bottom of 15 x 10 x 1-inch jelly-roll pan with nonstick cooking spray. Line bottom with waxed paper; coat paper with cooking spray.
Beat yolks and water in bowl on medium-low 1 minute. Beat in sugar and vanilla. Increase speed to high; beat 5 minutes, until ribbon forms when turned-off beaters are lifted.
Sift together flour, baking powder and salt into clean bowl.
Beat egg whites in clean medium-size bowl with clean beaters until soft peaks form.
Gradually sift flour mixture over yolk mixture; gently fold in until completely incorporated. Fold in beaten egg whites. Pour batter into prepared pan, quickly spreading in an even layer.
Bake in 350 degree F oven 20 to 22 minutes, until top is golden and springs back when lightly pressed with fingertip. (Cake may cook over edge of pan slightly.) Remove pan to rack; let cool completely. While cake is still warm, gently loosen edges of cake from pan. Leave cake in pan until ready to assemble semifreddo. Makes 12 servings.