In a bowl, combine the eggs with the carrot, celery and onion, if using. Mix the mayonnaise with the mustard and stir into the egg mixture. Season, to taste, with salt & pepper.
Lightly butter one side of the bread slices and assemble sandwiches.
Sandwich Butteflies:Cut a sandwich into quarters on the diagonal. Press smallest point of 2 triangular slices together to form butterfly shape. Lay a mini carrot stick onto joined point to form the “body”. Dot sandwich wings with mini carrot stick rounds, sliced radishes or sliced stuffed olives. Use chives set into egg salad to form antennae. Or simply prepare tea sandwiches, using a mix of white and wholewheat bread, crusts removed. Cut sandwiches into strips, squares or triangles.
Tip:You can purchase precooked eggs in grocery stores, however if working with raw eggs, the following method seems to produce bright yellow yolks with no discolouring. To cook eggs, place in a saucepan with cold water and set over high heat. When water comes to the boil, turn off the heat and let eggs sit in water for 20 minutes. Run eggs under cold water until chilled, peel shells and make egg salad filling.