Preheat the oven to 220°C and line a baking tray with baking parchment.
To make the choux paste, melt the butter in a saucepan, add 125ml water. Bring to the boil, remove from the heat and tip in the flour all at once. Add the salt. Beat quickly with a wooden spoon until the mixture comes away from the sides of the pan and forms a ball. Turn it onto a plate and spread out. Leave to cool for 3 minutes.
Return to the saucepan and beat the eggs in a little at a time until the paste is smooth and shiny – you may not need all the eggs. The paste must form soft peaks and not be too sloppy otherwise you will not be able to pipe it.
Spoon the mixture into a piping bag with a plain nozzle and pipe 2 inch lengths space about 2 inches apart, cut off from the piping bag with a knife. You should get 15 éclairs.
Bake one sheet at time until puffed and golden, about 12 minutes. Remove from the oven and pierce to release steam. Place in the oven again for a further 2 minutes to crisp up. Remove from the oven and allow to cool.
For a smooth consistency to your éclair filling, place 3 tbsp of blackcurrant jam in a saucepan and heat gently, when the jam is worm pass the jam through a sieve and leave to cool then fold into the crème fraiche. You may need to whisk the crème fraiche slightly to bring the consistency of whipped cream.
Slit open the éclairs and fill with the blackcurrant crème fraiche.
Add icing sugar to the blackcurrant jam and mix well to make an icing that holds its position.
Spoon over each éclair. Serve.