Peel the eggs and cut them in half lengthwise. Set the whites aside and put the yolks into a medium bowl.
Add the mayonnaise, lemon juice, mustard, and salt and pepper to the bowl and mash everything together with a potato masher.
Cut the egg whites into small, 1/4-inch pieces and add the whites into the egg yolk mixture. Next, add in the celery, chives, and dill and mix gently until the mixture is evenly mixed. Cover the salad with plastic wrap and chill for at least 30 minutes, and up to 1 day ahead of time.
Just before serving, season with salt and pepper.
FOR EGG SALAD SANDWICHES:
Place 3/4 cup of salad onto the bottom slice of a croissant. Use the back of a spoon to spread the mixture. Place a piece of lettuce on top of the salad followed by the top piece of the croissant. Repeat with the remaining salad, croissants, and lettuce.
The nutrition information that has been calculated for this recipe includes the croissants.