The Food52 site had some interesting ideas for how to use up the last bit of peanut butter in a jar rather than waste as I often have, by rinsing out the jar and running it through the dishwasher before it in recycling. It’s like using the pig from oink to tail.
Make a dressing out of it. Miso + peanut butter + chili sauce + apple cider vinegar for pasta salad, peanut butter + soy sauce + Sriracha + fish sauce for udon noodles or dipping. Soy sauce + garlic + sherry vinegar and you’ve got a marinade for tofu (or anything else).
We have done something similar for the end of a mustard bottle, adding some vinegar and making an emulsion for vinaigrette. They list others as well, but I like this particular idea for various dressings and sauces.
Lord knows, in our house there’s always an empty peanut butter jar. Now if only I could find a use for old milk bottles.