Start by placing your eggs in a single layer in a large pot. Cover them with cold water by at least an inch and bring the water to a gentle simmer over medium heat. Once the water reaches a simmer, cover the pot with a lid, turn off the heat, and let the eggs sit for 8 minutes to finish cooking gently. After that, move them immediately to an ice water bath to stop the cooking and make peeling easier.
Once the eggs are cooled, peel them under running water to help the shell slip off more easily. Use a sharp knife to chop the eggs into small pieces—don’t mash them. You want a chunky texture for the salad that gives each bite some structure and flavor. Transfer the chopped eggs into a mixing bowl to start building the salad base.
Add the mayonnaise, mustard, lemon juice, minced celery, red onion, white wine vinegar, tarragon, salt, and pepper to the bowl with the eggs. Gently fold everything together until well-combined, but avoid overmixing to preserve texture. Cover the bowl with plastic wrap and refrigerate the egg salad for at least 1 hour. This resting time allows the flavors to meld and the herbs to infuse the salad more deeply.
Chilling is especially important for texture and taste; warm egg salad can feel overly soft and lack flavor balance. Once cooled, give it a quick stir to make sure everything is still evenly mixed before assembling your sandwiches. The chilled salad also spreads better onto the bread.
Toast the bread slices in a toaster or a dry skillet until golden brown and firm. This step is essential to prevent soggy sandwiches and adds a nice crunch. Start assembling each sandwich with a layer of lettuce, followed by a generous spoonful of egg salad, a tomato slice, and some red onion if desired. Top with another lettuce leaf, then finish with the top slice of toasted bread.
Serve immediately for best texture and freshness. If packing for later, wrap the sandwich tightly and keep it chilled until serving. You can also add a slice of cheese or bacon for variations, though the classic version is perfect as-is.