Combine: Combine spinach, lemon zest, lemon juice, tarragon, parley, chives, garlic, and anchovy paste in a food processor and pulse until well chopped. It will resemble a rough chimichurri style sauce.
Mix: Add the mayonnaise, sour cream, and Greek yogurt and mix again with the food processor, just to combine. Salt and pepper to taste. Transfer to a bowl to serve.
