If you’re cooking your Pudding in the oven, start by preheating your oven at 325°F (160°C). If not, you can Double Steam your Flan too (described above)
Make the Caramel: take a saucepan, mix the sugar and water and cook over low heat, until it is a dark golden brown. It is optional here to add a shot of Espresso if you’re making an Espresso Caramel Custard.
When the Caramel is hot and runny, immediately put it into your dish. You can either divide the caramel among 4 small dishes (ramekins) or one big dish (like how I did it). Move the bowl(s) around so your caramel gets stuck on to the side surface of the bowl(s) as well.
Make the Custard: In another small saucepan combine, milk and sugar and heat them until the sugar has dissolved, do not boil. Castor Sugar dissolves faster than Granulated Sugar, so I would recommend that.
In a heatproof bowl, whisk together eggs and vanilla extract. Gradually pour hot milk into the bowl, while constantly whisking. Mix everything properly.
Pour the custard into the prepared bowl(s) on top of the caramel.
Now EITHER, place the bowl(s) in a large roasting tray. Carefully add the boiling water into the tray until it is halfway up the sides of the ramekins. Bake for about 40-45 minutes, or until lightly golden.
OR, take a wide but shallow vessel (something close to a kadhai), fill it with water and let the water boil. Place the bowl(s) in it. The water should not be able to get in and cover the entire vessel to let it steam cook.
Remove from the oven/vessel when done and let it cool down to room temperature.
Refrigerate for at least 1-2 hours, until chilled..
Before serving run a knife around the bowl, invert and serve when cold.