Preheat the oven to 180oC. Line a large baking tray with parchment.
Place the butter, salt, sugar and 125 milliliters of water into a small saucepan over a medium-high heat. Bring the mixture to a rolling boil, and when all the butter has melted, add the flour and vigorously beat the mixture with a wooden spoon until a smooth ball of dough forms.
Keep the pan on the heat and stir rapidly for a further minute. Tip the dough into a bowl and leave it to cool until it has stopped steaming. If the dough hasn't cooled properly when you add the egg, it will scramble.
Beat the eggs together briefly in a small jug. Add the eggs into the cooled dough in 3 separate additions, beating well in between each one. You might not need to add all the egg - when you are adding the final amount you want to add just enough so it falls of the spoon and leaves a 'v' shape. Spoon into a large piping bag fitted with an open star nozzle.
Line a ruler up next to the baking tray and pipe 12 x 10 centimeters eclairs onto the tray, making sure to leave enough space between each one for them to expand during baking. Use a wet finger to smooth over any bumps. Glaze each éclair with the egg using a pastry brush.
Bake for 25-30 minutes and then turn the oven off and leave the eclairs to dry out and cool completely in the oven. They should be golden brown and well risen.
Whip the cream, mint extract, icing sugar and food colouring into soft peaks and then carefully fold through the chopped chocolate chips. Spoon into a piping bag.
To make the glaze, melt the fondant, cocoa powder and 2 tablespoons of water in a wide saucepan until smooth.