There are two basic recipes, using either sliced or mashed eggs - try them both to see which you prefer.
How to Hard-Boil An Egg
For either sandwich variation, first you need to hard-boil your eggs. Choose the best eggs you can find. Free-range or organic eggs have a better flavour than battery eggs, as well as being humanely produced.
Have the eggs at room temperature, as they are far more likely to crack if taken straight from the fridge.
Use one egg per person for a generous amount of sandwich filling. Place the eggs in a small pan, cover with cold water , bring to the boil and cook for 6 minutes if you like your eggs slightly soft in the middle, or 7 if you prefer them fully set.
Guesswork is dangerous - an undercooked hard-boiled egg is messy and not pleasant to eat, and if overcooked the yolk will develop an unsightly black ring - use a kitchen timer.
When the cooking time is up, drain at once and refresh under the cold tap for at least a minute, then leave to stand in cold water for another couple of minutes, until cool enough to peel.
Egg Salad Sandwich with Sliced Egg
Peel the hard-boiled eggs, rinse to remove any fragments of shell and pat dry with kitchen paper.
Slice the eggs - a slicer is the easiest way to do this. Spread bread lightly with butter, or for a healthier option, use an olive-oil or sunflower-oil based spread, low fat or not, as you prefer.
Lay the slices on the bread, then top with salad. Watercress is a great partner for egg, or use torn leaves, and thinly sliced tomato or cucumber. Don't add tomato and cucumber unless the egg salad sandwich will be served straight away, as these tend to make the filling soggy if kept for too long.
Season lightly and top with a second slice of bread.
Egg Salad Sandwich with Mashed Egg
Hard-boil eggs as above, and peel. Place eggs in a small bowl and mash with mayonnaise (don't overdo the mayonnaise, as it's very high in fat - use a low fat variety if you prefer). You can use pesto instead of mayonnaise if you prefer - for homemade pesto, see how to make pesto.
Mashing the eggs makes them go further, and children often prefer them served this way, making these sandwiches a useful choice for lunch boxes for kids.
You'll find that that two eggs will make three rounds of sandwiches. Spread the mashed egg on to bread and top with salad as before. And there you have a delicious, healthy egg salad sandwich.