Sponge Sheet Cake
NOTE: Room
temperature eggs will increase more in volume than cold eggs, so
the whites and yolks are both warmed in a bowl set over a pan of
hot water before being beaten.
6 large eggs, separated
1/2 teaspoon cream of tartar
1/2 teaspoon salt
3 tablespoons plus 1/2 cup sugar
1 teaspoon vanilla extract
2 tablespoons hot water
1 cup plain cake flour
INSTRUCTIONS:
1. Adjust oven rack to center position and heat oven to 350 degrees. Lightly grease 18-by-11-inch jelly roll pan or 16-by-12-inch half sheet pan. Line bottom and sides of pan with wax paper, allowing 1-inch overhang on each end. Do not grease paper.
2. Place egg whites in large bowl and warm to room temperature over pan of hot water. Remove bowl with whites from hot water and whip with electric mixer at medium speed until foamy. Add cream of tartar and salt, increase mixer speed to medium-high, and beat whites to soft but definite peaks. Slowly sprinkle in 3 tablespoons sugar; continue to beat until whites are shiny and very thick, 3 to 4 minutes. Scrape whites into wide 4-quart mixing bowl.
3. Without washing bowl or beaters, add yolks. Warm to room temperature over pan of hot water. Remove bowl with yolks from hot water. Add vanilla and hot water; beat at high speed for 1 minute. Slowly add remaining 1/2 cup sugar; beat until mixture is pale, shiny, and almost as thick as marshmallow cream, 4 to 5 minutes longer.
4. Scrape yolk mixture over egg whites; gently fold with rubber spatula until about two-thirds mixed. Sift flour over egg mixture; gently fold until flour is completely incorporated. Spread batter into prepared pan, smoothing top with spatula. Bake until cake top is lightly browned and center springs back when lightly pressed, 12 to 15 minutes.
5. Remove pan from oven and immediately free cake edges from pan sides with knife. Smooth sheet of wax paper over cake top. Place another sheet pan or cookie sheet on top of cake. Flip over both pans and lift off baking pan with cake. Cool cake, then gently peel off wax paper from cake bottom, removing bottom crust. Flip cake, top side up, then peel off second sheet of wax paper, removing top crust. (Cake can be wrapped in plastic, then foil, and refrigerated for 1 day.)