Chiffon Cheesecake

Bought a 2-kg package of Australian cream cheese from Phoon Huat last month so that I can experiment different cheesecake recipes :) Gave some to my youngest sis SL whose also now into baking. It's more economical.
2 kg Australian Cream cheese at Phoon Huat $16.70
250g Philadephia Cream Cheese $5.00

I've borrowed a book from NLB all about cheesecakes "Fantastic Cheesecake" by Alex Goh.
I halved the recipe for the Chiffon Cheesecake & reduce the baking time to make a mini cake.

Mini Chiffon Cheesecake using mini-chiffon tin from Daiso

I've read up on tips by Rei on baking chiffon cakes before starting (http://allthatmatters2rei.blogspot.com/2008/06/chiffon-cake-tips-and-trouble.html).
She's has also included step-by-step pictures of baking a chiffon cake. So it was really useful.
As u can see from the picture of my chiffon cake, the sides of the cake has sunken in. I might have overbeaten the egg whites?
Taste Test: Hubby says it's very nice. But I find it a little sweet and texture not airy & light enough. So not really good...

Original Recipe for Chiffon Cheesecake
(Makes 1 9-inch chisson cake)

Ingredients:
(A)
60g milk
40g cream cheese
25g butter

(B)
65g flour

(C)
4 egg yolks

(D)
4 egg whites
100g sugar
a pinch of salt
1/8 tsp Cream of tartar

Method
1. Cook (A) over double-boiler until well blended & mixture thickens.
2. Remove from double-boiler. Add (B) flour & mix till smooth. (I used a whisk)
3. Add (C) egg yolks and mix till well combined.
4. In a oil-free mixing bowl, whip egg whites till foamy. Add in the rest of the ingredients in (D) & whip till stiff.
5. Add stiff egg white to the cream mixture & fold in gently till well incorporated.
6. Pour the batter into a 9-inch chiffon tin. Do NOT grease the pan. Bake at 175 degrees for 35-40 minutes.
7. Remove from oven. Invert the cake tin & cool the cake upside down.

Notes:
Make sure that mixing bowl is free from oil & egg yolk in order for proper whisking of egg whites.