Boil milk and butter, lower fire than add in cheese cream, use hand whisk to stir till smooth. Add in plain flour and corn flour mix well. And finally add in egg yolks and vanilla flavour, mix cheese cream mixture till thick and transfer to large bowl and leave to cool.
In a mixing bowl, whisk egg whites, cream of tar tar and sugar till peak form. Use a spatula to fold egg whites in two batches to cheese cream mixture.
Pour cheese cream mixture to a lined 9" square cake tin and steam bake at 150C for about one hour 15 mins.