Combine the endive, apples, blue cheese, onions, walnuts and tarragon in a medium mixing bowl. Add the Soy-Sherry Vinaigrette (use as much or as little as desired) and season with salt and pepper.
Puree the sherry vinegar, soy sauce, Dijon mustard, shallots and egg yolk in a blender. With the motor running, emulsify the oil into the mixture. Season with black pepper (the salt from the soy will be enough to season the vinaigrette).