This magical cake separates during the cooking process to a thick custard layer that sits below a spongy cake layer.
1/2 cup orange marmalade
125g butter, plus extra for greasing
4 eggs, separated
1/2 cup castor sugar
1 cup plain flour
1 tsp white vinegar
1/4 cup icing sugar
1. Heat your oven to 160ºC and line a 20cm square cake tin.
2. Combine the marmalade and butter in a small saucepan and heat until the butter is just melted. Set aside to cool slightly.
3. In the bowl of a stand mixer combine the egg yolks and sugar, beating until pale and fluffy. Add a tablespoon of cold water and the melted butter and marmalade mixture and whisk to combine.
4. Add the flour with the mixer set to a slow speed, and when it is incorporated add the milk a little a time until the mixture is smooth.
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 45 minutes or until the top is brown and the edges are well set. The cake should still be very wobbly in the centre.
6. Cool to room temperature in the tin, then chill in the fridge for 2 hours.
7. Remove, slice and dust with icing sugar to serve.