Mix together milk, cooking oil and salt in a bowl.

Place the bowl over water bath and keep stirring until the mixture turns warm.

Sieve cake flour into a bowl.

Add flour to warm milk mixture and mix.

Add egg yolks in batches and mix.

Add vanilla extract and mix well.

Beat egg whites until foamy.

Add vinegar and castor sugar in batches and beat until firm peak.

Transfer about ⅓ of the meringue to the egg yolk mixture and fold gently.

Add finely grated parmesan cheese and fold in gently.

Pour the mixture into the remaining meringue and mix gently with a whisk.

Give the pan a few taps on a hard surface to release air bubbles.

Line an 8 inch square pan with baking paper and pour in about half of the batter.

Spread the batter in the pan evenly with a chopstick.

Arrange slices of cheddar cheese to cover the batter but leave a small gap around the edges.

Add the remaining batter and cover the cheese completely.

Sprinkle finely grated parmesan cheese all over the top.

Put the pan of batter into another slightly bigger pan.

Place a tray of hot water at the bottom of an oven preheated to 160 C.

Bake for 20 mins at 160 C and lower to 150C and bake for another 40 to 50 mins at the lowest rack of the oven.

Test with a skewer and ensure that it comes out clean. Double check for doneness by pressing the surface of the cake gently with your finger or the back of a spoon. If it bounces back, the cake is fully cooked.

Cut and serve while it is still hot from the oven. Cake could also be refrigerated. Thaw before serving.