Place the 8 eggs in a single layer in a medium saucepan and add cold water to cover by about 1 inch (2.5 cm). Bring to a gentle boil over medium-high heat. Once boiling, reduce heat to maintain a simmer and cook for 10 minutes for firm yolks. Immediately transfer eggs to an ice bath (bowl of ice water) and cool for at least 5 minutes to stop cooking and make peeling easier.

Peel and chop

Tap each cooled egg gently on the counter, roll to crack the shell, and peel under running water if needed. Pat dry with paper towel. Roughly chop 6 eggs into 1/2-inch pieces and finely chop the remaining 2 eggs (reserve one yolk if you prefer chunkier texture—optional). Place chopped eggs in a medium mixing bowl.

Prepare mix-ins

While eggs cool, finely dice 1 celery stalk and mince 1 small shallot. Thinly slice 2 tablespoons chives and chop 1 tablespoon parsley. Measure out mayonnaise, Greek yogurt, Dijon, lemon juice, and apple cider vinegar.

Combine dressing and seasonings

In a small bowl, whisk together 3 tablespoons mayonnaise, 2 tablespoons Greek yogurt, 1 teaspoon Dijon mustard, 1 teaspoon lemon juice, and 1 teaspoon apple cider vinegar until smooth. Add 1 teaspoon celery salt, 1 teaspoon kosher salt, and 1 teaspoon freshly ground black pepper. Taste and adjust seasoning—add more lemon for brightness or a pinch more salt as needed.

Fold everything together

Pour the dressing over the chopped eggs. Add the diced celery, minced shallot, chopped parsley, and sliced chives. Gently fold with a rubber spatula or spoon until eggs are evenly coated but still have texture—avoid over-mixing to prevent a pasty result. If the mixture seems too thick, add up to 1 tablespoon additional mayonnaise or yogurt to reach desired creaminess.

Chill and finish

Cover the bowl and refrigerate the egg salad for at least 20–30 minutes to let flavors meld. Before serving, taste and adjust seasoning. Sprinkle 1/4 teaspoon smoked paprika over the top if using for color and a hint of smokiness.

To Serve

If toasting bread: lightly butter or brush 1 tablespoon of olive oil on both sides of 8 slices of bread. Toast in a skillet over medium heat 1–2 minutes per side until golden, or toast in a toaster until lightly crisp.

Assemble sandwiches: place a lettuce leaf on 4 bread slices (or bottom halves if using rolls), divide the egg salad into 4 equal portions (about 1 cup each) and spoon onto the lettuce. Top with tomato slices if using, then close with remaining bread slices.

Serve chilled or at cool room temperature: cut sandwiches in half if desired and serve immediately. Leftover egg salad keeps covered in the refrigerator for up to 3 days.