Clean and rinse fiddleheads. Blanch fiddleheads in boiling water for 1 minute. Remove from heat, drain and rinse in cold water to cool them. Clean and cut up peppers, wild leeks and fresh herbs.
Pour vinegar over cooled fiddleheads in a non-reactive container. Add cut up peppers, wild leeks, herbs, sugar and salt. Stir to wet all ingredients. Add Olive Oil and stir again. Refrigerate for 24 hours before serving.