• In a large saucepan over medium heat, sauté the onion and celery in the butter until translucent but not browned, 3 to 4 minutes.
• Add the fiddleheads, salt, and pepper and cook for 2 to 3 more minutes. Pick out 4 nice fiddleheads and set them aside to use as a garnish later.
• Add the chicken broth and bring to boil, then reduce the heat and simmer the soup for 15 minutes, with the lid ajar on the saucepan.
• Blend the soup in the saucepan with an immersion blender until creamy, or transfer it to a regular blender to purée (cover the lid of the blender with a tea towel and hold down the lid, as the soup will be hot and could cause the lid to pop off).
• Add the cream and simmer the soup for an additional minute to reheat it.
• Garnish each bowl with a reserved fiddlehead, and serve with chive toasts.

To make the chive toasts:

• Toast the bread slices, then spread each one with a thick layer of mayonnaise. Thinly slice the chives and pile them up on the toasts to completely cover the mayonnaise.