Preheat oven to 160°C. Lightly grease the pan with butter. (Just a little, as shown in the photo.)
Make the caramel. Heat the sugar and water in a saucepan.
When it starts to boil, and is the color shown in the photo, it will quickly turn dark brown. (Be careful not to burn it, or it will be bitter.)
Immediately pour the caramel into the cake pan.
Prepare the egg mixture. Put the whole egg, the egg yolks and sugar in a bowl and beat well with a whisk for 1-2 minutes.
Here is the key to making it taste even better! Heat up the whipping cream and milk in the same pan you used to make the caramel.
There will still be some caramel stuck to the saucepan, so heat it to about the temperature of bath water to melt it.
Carefully pour the egg mixture from Step 5 into the saucepan. Add a few drops of vanilla extract.
Pour the mixture from the saucepan in Step 8 through a strainer into the cake pan with caramel in the bottom.
Make the sponge cake batter. Beat the eggs and sugar in a bowl over a 50°C hot water bath.
Hint!! You will use hot water when you bake it in the oven, so heat enough water for both.
When the batter is warm to the touch, take it off the hot water bath and beat it on high speed with an electric hand mixer until it's pale and thick.
Another important point! Beat it on low speed for one minute at the end to blend.
Gently fold in the plain flour. Mix in the oil just before the batter is completely blended.
Pour the batter from Step 14 into the cake pan.
Put the cake pan in a 5 ml-deep hot water bath, and bake at 160°C for 28 minutes.
It's done when a bamboo skewer inserted comes out clean.
Cover with plastic wrap when it has cooled off, then put the pan in the refrigerator to chill.
When it's well chilled, run a bamboo skewer around the edge, and it will come out of the pan nice and clean.
Cover with a plate and invert the cake onto it.
The sponge layer, soaked in lots of caramel sauce, will be on the bottom. (Just looking at it will make you smile.)
You're all done!
I'm often asked what kind of cake pan to cook it in, but you can use any pan you happen to have, such as a pound cake pan, an 18 cm round pan or a ramekin.
I made this cake in a 20 cm square pan. If you use a pan larger than 15 cm, shorten the baking time and test it for doneness.
If you use a pan smaller than 15 cm, reduce the amount of batter you pour in the pan by about 1.5 cm, and shorten the baking time.
Story Behind this Recipe
I came up with this recipe because I really wanted to be able to make the kind of velvety smooth pudding cakes sold in cake shops at home.
By using the same pan you used to make the caramel to heat the milk and whipping cream, the caramel stuck to the pan will melt and tinge the cream the color of milk-tea. I think this makes it look like high class pudding.
If you want to reduce the amount of sugar, cut the sugar in the custard pudding mixture to 40 g.