Line two baking trays with baking parchment and draw 4 x 16cm lines on each piece of baking parchment. Allow space between each line as the éclairs will spread a bit. Turn the baking parchment over. Place 200ml cold water and butter into a medium size saucepan. Bring slowly to the boil, so the butter is completely melted.
Tip in the flour when the water is boiling really fast. Draw off the heat immediately and beat the mixture with a wooden spoon until thick and smooth and leaves the sides of the saucepan.
Allow to cool for 10 minutes, a quick method is to leave it in a sink filled with cold water. Once the mixture is cool, beat in the eggs a little at a time until shiny and smooth. Preheat the oven to 200C/Fan180/Gas Mark 6.
Place a 1 1/2cm plain piping nozzle into a piping bag. Fill the piping bag with the choux pastry. Squirt a little of the choux under the baking parchment at each corner of the baking tray, this will help stop the paper from sliding when you are piping. Pipe the pastry over the lines to create each éclair.
Place in the oven and bake for 25 minutes, then swap the trays around and bake for a further 10-15 minutes. Remove from the oven and place on a cooling rack. Allow to cool completely. Split the éclairs open with a serrated knife.
To make the icing, mix enough lemon juice and food colouring, to your colour preference, into the icing sugar. Mix until smooth, the mixture should be just runny. Spoon the icing over the top and length of the éclair lids.
Whisk the cream until thick. Place a 1cm piping nozzle into a piping bag and fill with the cream. Pipe the cream on to the bottom half of the éclairs.
Put the lemon lids back on top of the cream and bottom half of the éclairs. Decorate with thyme sprigs. Serve straight away.