Place prunes in a heatproof bowl. Pour boiling hot water over prunes and allow prunes to soak for at least one hour, up to overnight.
Remove prunes from liquid, saving water to use to thin out sauce later.
Place plumped prunes into a blender or food processor. Add miso, tamari, rice vinegar, Chinese five spice powder, minced garlic, and ¼ cup water. Pulse to combine, then blend. Add more water 1 teaspoon at a time to thin the sauce, about the consistency of Ranch dressing.
Make Hoisin Peanut Dipping Sauce
In a bowl, whisk together Homemade Hoisin Sauce, peanut butter, garlic, and lime juice. Add water to thin out sauce into a dippable consistency.
Transfer Hoisin Peanut Dipping Sauce to serving bowl and garnish with coarsely chopped roasted salted peanuts, or whichever nut butter you used in the sauce.