Lemon Soufflé Cake [1st Attempt]

After baking the Orange Souffle Cake and Chocolate Souffle Cake which I like so much, I again tried with lemon flavour.  The flavour of this cake is very refreshing and the texture is soft, cottony and moist. 
The only mistake I made was I covered the top with foil but forgotten to extend the baking time for another 10 minutes.  So the top was a little moist and difficult to handle.  I then grilled it for about 5-10 minutes to make it easier for slicing, the cake was saved.   Don't follow this way, unless you prefer a pale crust.     Next time, I will try to bake at 180 degrees C for 45 minutes if I'm covering it with foil.

Ingredients

3 egg yolk
1/2 egg (about 30g)
15 gm sugar [I used 1 tbsp]
1/4 tsp salt
25 ml lemon juice
25 ml milk
1 tsp lemon zest
35 ml vegetable oil [I  used 1 1/2 tbsp]
40 gm cake flour  - sifted - set aside

3 egg white
55 gm sugar [used 3 tbsp]
1/4 tsp cream of tartar

1. Line base of a 7" square tin [use loose bottom pan] with grease proof paper and wrap it with tin foil.  Place it in a bigger square baking tin.  Preheat oven to 150 degrees C.
2. Mix lemon juice, milk, lemon zest and oil  together.
3. Use a hand whisk mix egg yolks, half egg, sugar and salt together.
4. Add in liquid mixture and whisk until well combined.
5. Fold in sifted flour and stir until batter is smooth.
6. Use a cake mixer, whisk egg whites and cream of tartar till frothy.   Add in the sugar in 3 batches and whisk on medium speed until soft peaks formed.
7. Fold in 1/4 of the meringue into the egg yolk mixture until combined.   Then fold in the rest of the meringue lightly in two portions until well combined.
8. Scoop out 1/3 of mixture, add a little [1-2 drops] of green colouring, fold until combined.
9. Pour 1/3 of plain batter into prepared cake tin, followed by green batter then again the plain batter.  Place it in the bigger cake tin filled with hot water.
10. Steam-bake cake in a preheated oven at 150 C for 55-60 minutes [without covering with foil.  [If covering cake with foil, bake at 180 degrees C for  45 minutes, after 45 minutes, remove foil and bake a further 10 minutes].
11. Remove cake at once from tin, discard all paper linings [to prevent vapour when cooling] and cool it on a wire rack.