Sponge Cake With Orange Flavour

Sponge Cake

Ingredients:
6 large eggs, separated (use cold eggs)
1 cup sifted all-purpose flour (make sure you sift the flour before measuring it)
1/4 tsp baking powder
1/4 tsp salt
1 cup granulated white sugar
3/4 tsp white vinegar
1 tsp vanilla extract
2 tbsp water
Zest of 1 big orange
Method:
Separate the cold eggs. Place the yolks and the whites in separate bowls, cover them with a plastic wrap and bring it to room temperature. This may take around 30 mins.
Pr-heat oven to 180 degrees C or 350 degrees F and place the rack in the center of oven.
Sift or whisk together flour, baking powder and salt.
Place the egg yolks and 2/3 cup of sugar in a bowl and use a hand mixer to beat this. Beat on high speed until it is thick, fluffy and light coloured. When you raise the beater the batter will fall back into the bowl in a slow ribbon like form.
Now beat in the vanilla extract, orange zest, and water.
In a separate bowl whip the egg whites until foamy (use hand mixer). Beat just to break the egg whites. Make sure the bowl and the whisk is clean and non-greasy. 
Now add the white vinegar and beat until soft peaks form. Vinegar is used to stabilize egg whites.
Gradually add1/3 cup of sugar and continue beating until the egg whites are shiny and just form stiff peaks.
Now add the flour mixture to the beaten egg yolks. Add 1/3 of the flour mixture at a time and gently but quickly fold the flour into the egg yolks batter. Use a spatula or a wire whisk to do so. 
Gently fold little egg whites to the batter just to lighten it.
Now fold in the rest of the egg whites. Fold just until incorporated. Do not over mix the batter or it will deflate.
Take an un-greased two piece 10 inch tube pan. Pour the batter in this. Smoothen the top.
Bake for 25-35 mins or until a toothpick inserted at the center of the cake comes out clean.
Remove from oven and immediately turn it upside down and suspend it by placing the inner tube on the top of a flat topped glass or bowl.
 Let the cake cool completely before removing it.
Run a spatula or sharp knife around the inside of the pan to remove the cake. Do the same for the center and the bottom also.
Invert the cake onto a greased wire rack. The top of the cake will be sticky.
Sponge cake is ready to be served.
Tips:
Using cake flour will give better texture to this cake. 
You can use lemon juice or cream of tartar in place of white vinegar. 
You can use lemon zest in place of orange zest to make a lemon sponge cake.

Sponge Cake

Adapted from Stephanie Jaworski's recipe.