Roughly chop parsley, tarragon, chives, and green onions. Mince garlic and anchovy fillets if using whole fillets instead of paste.
1 cup fresh parsley leaves, 3 tablespoons fresh tarragon, 3 tablespoons fresh chives, 2 green onions, 1 clove garlic, 2 fillets anchovy fillets
Add herbs, garlic, and anchovy to blender or food processor. Pulse 5-6 times until finely chopped but not pureed, scraping down sides between pulses.
1 cup fresh parsley leaves, 3 tablespoons fresh tarragon, 3 tablespoons fresh chives, 2 green onions, 1 clove garlic, 2 fillets anchovy fillets
Add mayonnaise, sour cream, olive oil, and lemon juice to the blender. Blend on low for 10-15 seconds until smooth with no visible herb chunks.
0.75 cup mayonnaise, 0.5 cup sour cream, 1 tablespoon olive oil, 2 tablespoons lemon juice
Add salt and black pepper to taste. Blend for 5 seconds to incorporate seasoning. Taste and adjust lemon juice or salt if needed.
salt, black pepper, 2 tablespoons lemon juice
Transfer dressing to an airtight container and refrigerate for at least 60 minutes. Stir before serving to recombine if any separation occurs.