Preheat oven to 375°. Line bottom and sides of a 13- x 9-inch pan with aluminum foil, allowing 2 to 3 inches to extend over sides of pan. (Do not grease pan or foil.) Sift together first 3 ingredients.

Beat egg whites and cream of tartar at high speed with a heavy-duty electric stand mixer until stiff peaks form. Gradually fold in sugar mixture, 1/3 cup at a time, folding just until blended after each addition. Fold in vanilla and lemon juice. Spoon batter into prepared pan. (Pan will be very full. The batter will reach almost to the top of the pan.)

Bake at 375° on an oven rack one-third up from bottom of oven 30 to 35 minutes or until a wooden pick inserted in center of cake comes out clean. Invert cake onto a lightly greased wire rack; let cool, with pan over cake, 1 hour or until completely cool. Remove pan; peel foil off cake. Transfer cake to a serving platter. Spread Lemon-Cream Cheese Frosting evenly over top of cake. Garnish, if desired.