1. In a small dry skillet toast the rosemary and thyme until fragrant, do not burn. Shake the skillet and heat for about 3 minutes. Set aside.
2. In a large saucepan saute onion, celery and carrots in olive oil over moderately low heat for about 1 minute, stirring constantly.
3. Stir in the broth or stock and bring to a boil.
4. Break potatoes up with a fork. Using a wire whisk, add potatoes a half cup at a time.
5. Continue whisking until smooth, reduce to a simmer and add toasted herbs, lemon juice and fresh parsley.
6. Taste soup and add salt and black pepper if desired.