Step 1

Preheat oven to 350 F. In a medium bowl, combine flour, salt and baking powder. In the bowl of a stand mixer, whisk the egg whites on medium speed until frothy. Add the cream of tartar and continue to whisk until egg whites form firm peaks that hold its shape when the whisk is lifted.

Step 2

Meanwhile, beat the egg yolks in another bowl until it is slightly thicker. Add the sugar and mix until incorporated. Add water, oil and vanilla extract. Mix well.

Step 3

Add flour mixture gradually to the yolk mixture and mix until the batter is smooth. Gently fold the egg whites to the yolk batter in three additions until batter is uniform. Pour batter into an ungreased10-inch tube pan. Bake for 55-65 minutes, or until a toothpick inserted in the middle of the cake comes out clean. Set tube pan top of two overturned mugs  and let cool.

Step 4

To unmold cake, loosen sides and bottom with a knife. Using your hands, gently press the sides of the cake downwards to loosen it more. remove gently and invert to a serving plate.