In a small saucepan heat the caramel ingredients over medium heat. Meanwhile, prepare a large bowl of iced water.
Once the caramel has turned amber (roughly 3-5 minutes), take the saucepan off the heat and place into the bowl of iced water for 10 seconds. Be careful not to splash any icebath water into the caramel.
Pour or spoon the caramel into the moulds and leave to harden.
Whisk the eggs in a medium-sized bowl and set aside.
Put the milk, sugar, vanilla and salt into a medium-sized saucepan over medium heat. Stir until combined and all the sugar has dissolved, then keep heating until the mixture reaches 70 C / 158 F.
Preheat the oven to 150C / 300 F.
Take the milk mixture off the heat and add the eggs slowly through a strainer. Mix until completely incorporated.
Strain the mixture again, then pour into the moulds. Place a tea towel on your workbench and tap the moulds onto the towel a few times to remove any air bubbles. Cover in aluminium foil, and poke a few holes through the foil on each ramekin.
In a baking tray, lay down a tea towel. Put the moulds into the baking tray and fill the tray half way up the moulds with medium-hot water from the tap. Do not use boiling water!
Bake the flan for 35 minutes.
Take the moulds out of the baking tray and let them cool for 10 minutes at room temperature. Carefully remove the aluminium foil off and leave until cool enough to be handled.
Cover each mould with cling wrap and let it set in the fridge for at least four hours (though preferably at least 1 day) (Note 1).
Once ready to serve, run a knife around the edges to unmould the flan, and turn it upside down on a plate. The caramel will spill over the custard.