Simmer shallots in butter in a frying pan over medium heat for about 10 min or until soft. Toss in carrots, leeks and fiddleheads. Add stock, salt and pepper to taste and bring to a boil. Simmer for 30 min. Mix cream and egg yolks in blender. Pour into soup. Heat slowly. Do not boil. Boil remaining fiddleheads uncovered in salted water for 6 min. Drain. Serve in tureen. Sprinkle cooked fiddleheads on top as garnish.