1. Heat your oven to 160C and grease and line a 20cm square cake tin. Place 3/4 cup of the sugar in a saucepan over medium heat. Cook the sugar until it becomes a dark, liquid caramel, swirling occasionally to ensure it cooks evenly and doesn't burn.

2. Reduce the heat a little, add  1/2 a cup of water and whisk for a minute or two until the caramel is dissolved. Set aside for 5 minutes, then whisk in the milk and strain.

3. In the bowl of a stand mixer, combine the egg yolks and 1/4 cup sugar, beating until pale and fluffy. Add a tablespoon of cold water and the warm butter and whisk to combine.

4. With the mixer set to a  slow speed, add the flour, salt and two tablespoons of  cocoa, and add the caramel milk a little at a time until the mixture is smooth. Pass the mixture through a sieve to remove  lumps.

5. Separately whip the egg whites to firm peaks and add the vinegar, whisking to combine. Fold half the egg whites into the batter mixture until combined, then fold in the remaining egg white. Transfer to the cake tin and bake for 30-40 minutes or until the top is brown and the edges  well set. The cake should still be  wobbly in the centre.

6. Cool to room temperature in the tin, then chill in the fridge for at least two hours. Remove from the tin and dust with the remaining cocoa mixed with the icing sugar to serve.

The original: Adam Liaw's magical marmalade custard layer cake

Also try: Adam's Japanese-style German honey cake