Spray 10-inch jelly-roll pan with nonstick spray, dust with flour, and line with parchment paper.
Combine cake flour, cornstarch, and salt in medium bowl, sift three times.
With electric mixer on medium speed, beat the egg whites in large bowl until thick and foamy.
Gradually sprinkle in the sugar and cream of tartar.
Continue beating until the egg whites form medium peaks, 3-5 minute.
Add the flour mixture in 3 additions, gently folding each addition into the egg whites until well combined.
Fold in the butter, vanilla, if using, fold in the walnuts, citrus zest, and almond extract.
Pour the batter in the pan.
Bake until toothpick inserted comes out clean and cake begins to pull away from the sides of the pan, about 25 minute.
Cool the cake in the pan for 10 minute.
Remove from pan and cool completely.
Variation: For chocolate sponge cake, replace 1/4 cup of the cake flour with 1/4 dutch unsweetened cocoa powder, plus 1/2 tsp instant espresso powder.
Optional topping (may increase points): Combine 1/2 cup water with 1/2 cup sugar in saucepan, and bring to a boil. Remove syrup from heat and let stand until cool. Syrup can be flavored with dissolved espresso powder, run, or any type of liqueur.