Preheat you oven to 180C / Gas mark 4.
Place the milk, water, butter, sugar and salt into a medium sized saucepan and bring to a boil over a medium heat.
Take off the heat and immediately add the flour and mix vigorously with a wooden spoon until really smooth.
Then return to the heat and cook for about a minute. Until the mixture comes away from the side of the pan.
Remove from the heat again and wait around 1 minute before adding the egg, as you don’t want scrambled egg you need this small amount of cooling time. Whisk the egg into the mixture until you have a nice smooth batter.
Now put the mixture into a piping bag and pipe the éclairs out onto greaseproof paper on a baking tray. Leave a little room between them for spreading out a little.
Pop them into the oven for 25 to 30 minutes.
I found just before the time was up I needed to turn them over in the oven and give them a couple of minutes on the other side to fully dry the pastry out.
Once done take them out, pearce the end with a sharp knife so the steam can escape and cool them fully on a cooling rack.