Instructions

1. Preheat the oven to 325°F (162°C). In a large bowl, combine the flour, sugar, baking powder and salt. Make a well in the center; add the water, egg yolks, oil, lemon zest and vanilla. Whisk the dry ingredients into the yolk mixture until the batter is blended and smooth. Set aside.
2. In a large mixer bowl, beat the egg whites and the cream of tartar at medium-low speed until foamy. Gradually increase the speed to high and beat the whites until stiff (but not dry) peaks form. Gently fold 1/3 of the beaten whites into the batter with a rubber spatula just until blended. Fold in the remaining whites just until combined. Pour the batter into an ungreased tube pan or bundt pan. (I used bundt pan because I don't have a tube pan).
3. Bake 1 hour, or until the top springs back when lightly touched with a fingertip and a cake tester inserted into the center comes out clean.