Have all ingredients at room temperature, 68┬░ to 70┬░F. Preheat the oven to 325┬░F. Have ready 1 ungreased 10-inch tube pan with a removable bottom. Sift together twice into a large bowl:
2 1/4 cups sifted cake flour
3/4 cups sugar
1 tablespoon baking powder
1 teaspoon salt
In another bowl, beat on high speed until smooth:
3/4 cup water
2/3 cup vegetable oil
1 teaspoon grated lemon zest
1 teaspoon vanilla
Stir into the flour mixture until smooth. In another large bowl, beat on medium speed until soft peaks form:
9 large egg whites
1/2 teaspoon cream of tartar
Gradually add, beating on high speed:
1/2 cup sugar
Beat until the peaks are stiff but not dry. Use a rubber spatula to fold one-quarter of the egg whites into the egg yolk mixture, then fold in the remaining whites. Scrape the batter into the pan and spread evenly. Bake until the top springs back when lightly pressed and a toothpick inserted into the center comes out clean, 55 to 65 minutes. Let cool upside down for at least 1 1/2 hours, setting the tube over a bottleneck or resting the pan on 4 glasses. Unmold. Ice with:
