from Madhur Jaffrey's World of the East Vegetarian Cookbook. I eat this so often I've scaled up the original recipe for the sauce six-fold and boil a pound of noodles at one time, sprinkle on a little sesame oil & shake thoroughly to minimize sticking, then refrigerate. One jar of sauce lasts through two to four pounds of noodles. The noodles go bad faster than the sauce, and larger batches are a pain to boil anyway. I prefer to use a lot less water than in the original sauce; YMMV. I prefer udon noodles with this, but can't find an economical source around here. I find thin noodles don't work well, so I choose Chinese or Korean or Japanese noodles of various types, as long as they're medium width.
1-1/2 cups roasted, salted peanuts (non-salted is fine)
3 oz Sesame oil (use a darker, less refined brand for more flavor; toasted sesame oil OK but lots more expensive)
3 oz thin/light soy sauce (Chinese-style, not Japanese)
3 oz peanut oil
2 oz Chinese black vinegar (lots of variation among brands; add this last, using only 1oz, then add more to taste)
2 T sugar
1-1/2 t dehydrated garlic (garlic powder, equivalent to 6 cloves fresh garlic)
3/4 t cayenne pepper (or to taste; the final recipe has only a little hot aftertaste)
1/4 to 1-1/2 c water
Just blend them all together -- I use an immersion mixer in a jar. With no added water, the mixing just never seems to finish. Adding a little water gives better blending and chopping action, with only tiny bits of peanuts left. 1/4-1/3 cup works for me.
Fresh garlic doesn't blend into the sauce all that well; if you're going to use garlic powder, use it in sauces where it doesn't need to be cooked & save the fresh cloves for hot dishes.
The hardest thing to get right is the black vinegar -- the first one I tried was too strong, had to add more sugar to balance. A brand with a weaker titer of acid gave better taste. Black vinegar is sometimes sold diluted (marked as such) and a diluted, sweetened brand from Taiwan worked very well, with a quite different, but still very good, final flavor. If you prefer really piquant, avoid the sweetened variety, or leave out some sugar. I did try Bragg's Liquid Aminos once, need to try it again without sugar. Then you could use rice or sweet potato noodles (not sure how good that would taste) and make it gluten-free (many soy sauces now have added wheat or wheat flour; check the label carefully. Japanese soy sauce has long included wheat as standard).
Google "cold peanut noodles" for more recipes, of considerable variety. Also check any of Madhur Jaffrey's cookbooks -- not all are vegetarian, but lots of varieties of Asian cooking. Of course, Indian cuisine is her forte.