In a pan, add 235ml of the milk, salt and vanilla pod cut lengthways and its scraped seeds. Simmer the milk until small bubbles form around the edges, switch off the heat and allow it almost cool. Pass through a sieve
In a standing mixer, whisk the egg yolks and sugar until the egg mixture is light, pale and fluffy
With the mixer running slowly, drizzle the almost cold milk mixture into the egg mixture. Combine this mixture well. The milk should be almost cold, so this mixture doesn't become scrambled eggs!
Once the mixture is well combined, slowly pour in the rest of the milk and double cream
Pour the mixture back into the pan and simmer, stirring until the mixture thickens and coats the back of a spoon - this should take 10-15 minutes
Place the mixture in the fridge overnight and churn in an ice cream machine the next day
For the espresso sauce, mix the water, sugar and strong coffee in a pan over low heat and let the sugar dissolve completely and thicken the liquid, forming a syrup
Switch off the heat and add the coffee liqueur. Serve warm or cold over the panna cotta Ice cream