Simply mix the chicken – it should be quite finely chopped, otherwise the sandwiches are rather chunky – with the mayonnaise, tarragon, lemon and pepper. You are unlikely to need salt as most mayonnaises are quite salty but do check the mixture for seasoning. Butter the bread and make the sandwiches. Cut the crusts off each round, then cut each round into 4 fingers.
If you want a little more greenery in these you can use watercress leaves.