Preheat oven to 200°C and line a baking tray with greaseproof paper.
Mix the butter, milk and sugar together in saucepan and bring to the boil. Add the flour into the hot mixture and use a wooden spoon to stir the flour through till well combined.
Pour the mixture into a mixing bowl, slowly add the eggs and combine until smooth.
Place in a piping bag with a 10mm nozzle, pipe out a 5cm line onto the prepared tray.
Bake for 20 to 25 minutes or until golden brown. Remove from the oven, set aside to cool.
Meanwhile, make the filling by whipping half of the cream, then set aside.
Melt the dark chocolate in a metal bowl over hot water, careful not to allow any water to come into contact with the chocolate.
Slowly add the cream, stirring until combined. Add the coffee caramel sauce to the cream and combine.
To finish the éclairs, melt the dark chocolate as per method above and whisk in the remainder of the fresh cream. Stir until combined.
Dip the top of the éclairs into the chocolate, place on a tray and allow to cool.
Once the éclairs are cool, cut them in half and pipe the filling into them. Sprinkle a tiny amount of the sea salt onto the cream.