The day before making the sandwiches, remove the chicken from its packaging. Cover. Place the onion, bay, cloves, carrot, celery, and a pinch of salt in a saucepan and fill three quarters with cold water. Bring to the boil and simmer for 30 minutes to release the flavour from the vegetables. Add the chicken and simmer for 15 minutes. Remove from the heat. Allow to cool, then pour into a container and refrigerate.
he following day remove the butter from the fridge to soften. Drain the chicken. (You can save the liquid for stock.)
Make the mayonnaise by separating the eggs and placing the yolks in a small bowl sitting on a damp cloth on the bench. The cloth will keep the bowl steady when whisking. (Use the whites to make an omelette or add to a souffle.) Add the Dijon mustard, lemon juice and a good pinch of salt. Whisk together. Then, very gradually, add the oil while continually whisking. Start by adding a drop at a time and mixing each drop in well. Soon the mayonnaise will thicken a little and you can increase the flow to a slow trickle. Keep whisking until the oil has been absorbed and you have a mayonnaise. Refrigerate.
Cut the chicken into 1cm cubes and fold through the mayonnaise. Season, cover and refrigerate. Generously butter one side of each slice of bread. Add a layer of green leaves on one side of six slices then cover with six equal portions of the chicken and mayo mix. Season. Cover with the other sliced of bread, cut off the crusts (optional) and slice into triangles or ribbon sandwiches. Serve immediately or wrap tightly in cling film and refrigerate.
