Place a small saucepan over medium heat and add the sugar. Let the sugar turn into a dark caramel colour. Swirl the saucepan a couple of times to catch all the sugar and so that any part of the caramel burns. Pour the shot of water and swirl the pan 4 times at least for the caramel to homogenise. Pour the caramel into the bottom of the mould and swirl the mould for the caramel to go over the walls at least 1 cm. Set aside while we prepare the mixture.
Whisk the eggs and the egg yolk in a bowl, then whisk in the condensed milk. Follow by whisking in the milk and the vanilla flavouring. This can be done with a hand blender or even a jug blender, it makes very little difference.
Pour the custard mixture into the mould, being careful that the caramel doesn’t lift off from the bottom, help yourself by pouring it into a spoon before it touches the caramel if necessary.
In a large enough pot to hold the mould inside, pour enough water to cover the mould until at least half the height of the mixture within the mould. Place the mould carefully inside it with the water and cook it with the lid on (or a plate if you don’t have a lid) at a heat low enough for the water not to simmer (you have to judge it yourself as every burner, pot and everything else is different in each house) for 30 minutes or until you can clearly see that the middle of the “flan” it is set by moving the mould and watching the wave. This way of cooking it is called Baine Marie and can be achieved in a roasting tray in the oven at 160 degrees for about 40 minutes without any covering, again, check every now and then to see how it goes.