¼cupverjus (sour grape juice), or 2 tablespoons cider vinegar
Finely ground pepper
Tear the bread into small pieces to make about 6cups. Soak the bread in water long enough for it to become wet all over. Press out the excess water. You should have about 2cups.
In a mortar or on a work surface, crush the garlic with the salt until mashed to a puree.
Scrape the garlic puree into a blender or food processor. Add the olive oil and verjus. Blend while counting to ten, then add ⅓cup warm water and continue blending until smooth. Correct the seasoning with pepper and additional salt if needed. Scrape into a bowl, cover, and refrigerate overnight.