Preheat the oven to 160C. Grease and line a baking tin with baking papers. If the tin is loose based, wrap the bottom of the tin with double layers of aluminium foil.
In a heatproof bowl, add the cream cheese, butter and milk. Place over a pot of simmering water and stir to melt until combined.
Remove the bowl from the pot and leave to cool slightly. Add in the egg yolks and fold with a whisk until combined.
Add in the flours, salt and lemon juice. Fold until combined. Set aside.
To make the meringue, place the egg whites and cream of tartar in a stand mixer bowl. Beat until foamy.
Gradually pour in the sugar and beat until soft peaks forms.
Add 1/3 of the meringue into the cream cheese mixture. With a spatula or a whisk, gently fold in until incorporated. Fold in the rest of the mixture in 2 batches until incorporated.
Pour the batter into the prepared baking tin. Place it onto another baking dish, pour in hot water up to halfway of the baking tin. This water bath helps to keep the cake moist.
Bake in the preheated oven for 1 hour 10 minutes until the top is golden and the cake is set. Open the oven door slightly and leave the cake to cool down in the oven for 1 hour. This is because the sudden change of temperature will cause the cake to drop drastically. However, it is normal for the cake to shrink slightly after it has cooled down.
Refrigerate the cake for at least for 4 hours before slicing to serve.