Boil 4 or 5 jalepenos and about 1/2 of a chopped onion until the peppers turn light green. Cut the stems off the peppers.
Take the peppers and onions (save the water) and put them in a blender with a handful of rinsed celantro and chop it up some.
Don't lean over the blender when you open it up!
Then add a can of whole, peeled tomatos, 1/2 a spoon of garlic, a little salt, a little lime juice, and a little of the water you saved. You can use garlic powder if you don't have a jar, but not as good.
Blend that a little, just enough to mix it good. Don't want it too watery.
Best thing to do is just keep experimenting till you get something you like.