Classic Hungarian Sponge Cake

This is a classic sponge cake recipe, they teach this in pastry schools.
The listed ingredients are for a 23cm round cake pan.
Ingredients:
6 Large Whole Eggs - separated yolk and whites
120g White/Caster Sugar
120g All Purpose Flour/ Plain Flour / BL55
Preparation:
Pre heat he oven to 160degC fan forced.
Wrap the cake ring in baking paper, i covered the base of the cake ring (as i have a removable base ring) and butter the sides and dust lightly with flour.
The Making:
Beat the egg yolks until light a fluffy. Optionally add some vanilla extract.
Beat the egg whites, and gently gradually add the sugar as you are beating it. Add a pinch of salt. The texture should be not hard and stiff, but rather sour cream like, soft and smooth.
Mix the beaten egg yolks with the egg whites gently.
Gently mix in the flour through a sieve, make sure no lumps.
Pour mixture into the prepared cake pan.
Pull the cake mix sides up towards the side of the cake pan. This way eliminating the centre of the cake to pop up unevenly in the middle.
Bake at 160degC for 40 minutes.
Variations:
Walnut - Add 20g fine ground walnut to the flour (deduct the amount from the total flour mixture weight) so you will use 100g flour plus 20g ground walnut.
Cocoa - Add 10g good quality unsweetened cocoa powder to the flour, again deduct the cocoa powder weight from the total flour, this case you use 110g flour plus 10g cocoa.
Lemon - Use one whole lemon or Orange (or mix of two, half/half) finely grated skin, add this to the egg yolk mixture before beating.
Make your own filling as you desire, wether is chocolate, vanilla, or fruit based cream.