Grease and line the bottom and sides of a 20-cm springform cake pan. Wrap the outside of the pan with foil. Make sure the foil comes up all around the sides to about half the height of the pan. Pre-heat oven to 160 deg C. Prepare a water bath by filling a baking tray large enough to hold the cake pan, with water. Fill the pan up to a height between 2 to 2.5 cm, with water.
Place A in a mixing bowl and stir over double boiler (read notes below) until mixture becomes thickened, almost like custard. Remove from double boiler.
Add B and mix until well combined. Add C, one yolk at a time, mix until well blended.
In a dry mixer bowl, whip egg whites in D until foamy. Then add the cream of tartar. Then add sugar in a slow, continuous stream, and lastly, salt. Continue whipping until soft peaks.
Fold the egg white mixture from (4) into the cheese mixture from (3) above, until well incorporated.
Pour the cheese filling into the prepared cake pan. Bake in water bath at 160 deg C for 45 to 60 mins. The cake is done when firm and golden brown. Test if cake has completely baked through by inserting a bamboo skewer in the centre of the cake. It should come out clean.
Remove cake from the oven. Remove the cake from the mould immediately. Set aside to cool.
In step (2), a double boiler or bain-marie is easily set up in any kitchen. Just fill a saucepan or small pot with about an inch of water. Make sure your mixing bowl containing the ingredients you wish to heat, can sit over the saucepan or pot, with the base of the mixing bowl about an inch ABOVE the water level. If the water level is too high or too low, just add or remove water as required, but you should have about an inch of water in the saucepan or pot.
When heating the cream cheese mixture, the mixture will be somewhat lumpy. Just do your best to break down the bigger lumps but don't worry about the smaller or tiny lumps. These will smoothen out when combined with the flours.