Place all the herbs, the spinach, shallot, anchovies, salt, white pepper, and water in the bowl of a food processor. Blend together until the mixture forms a paste. Add the vinegar, yogurt, mayonnaise, and mustard and slowly blend together well. With the processor on a low speed, slowly drizzle in the oil in a slow stream until the dressing is emulsified. Add the lemon juice, Worcestershire, and Tabasco (if using), and blend together well. Store in a tightly covered container in the refrigerator for at least 2 hours before using. Will keep for up to 1 week.
Like many salad dressings, it’s optimal to make this a day before serving, to let the flavors meld and reach their peak. If you can’t manage a full day, at least make it 2 hours before you use it. It’s best to make it in a food processor so it will come out very smooth and emulsified. However, it is possible to make by hand or with an immersion blender; if you do, be sure to chop all the herbs, the shallot, and the anchovies very, very finely, with a mezzaluna or sharp chef’s knife, before blending together