Note: you will need 4 large dariole molds of approx. 175ml
Preheat the oven to 150C/gas mark 2.
Pour the milk into a measuring jug and add the 4 espresso coffees. Now top up this mixture with double cream until it reaches 600mls.
Pour into a stainless steel pan and add the coffee beans and salt. Warm together, occasionally stirring, until just below simmering point, and add the vanilla extract.
Switch off the heat, cover with a lid and leave to infuse for at least 2 hours
Now to make the caramel, put the granulated sugar in a solid-based saucepan and add 3-4 tablespoons of water. Bring to a simmer and cook slowly until the sugar has become a richly coloured caramel (using a light coloured pan helps you to see the colour of the caramel developing); take care during the final stages, so as not to burn it.
Pour into the base of the dariole molds, dividing the caramel between them. Leave to cool.
Put the eggs, yolks and caster sugar into a roomy bowl, whisk together lightly and then strain over the coffee-infused milk [discard the exhausted beans].
Gently whisk together [not vigorously] until well blended. Remove any froth with a piece of kitchen paper, then ladle the mixture into the caramel-lined molds and fill to the brim.
Place them in a deep roasting tin and fill with tap-hot water, so that it rises up the outside of the molds by about three-quarters.
Carefully slide the tin into the oven and loosely lay a tent of tin foil over the surface of the molds, but do not secure it down. Bake in the oven until the custards are set; about 40-45 minutes. To check, lightly press a finger on the surface, or give them a little shake: they should wobble.
Remove from the oven, take out from the roasting tin and leave to cool. When quite cold, cover each custard with a small sheet of clingfilm and put in the fridge for at least three hours.
To unmold, run a small knife around the edge of the custard and upend onto individual, shallow dishes. Eat with a teaspoon - and with great pleasure.