An Argentine co-worker gave me the following recipe, although she was very clear that this is what her family likes, and that every family has their own variation. Many versions have much more oil, and just the flavored oil is used and the solids are either strained out or left in the bottom of the container and topped off with more oil for the next meal.

Here goes (all total approximations):

In a food processor, combine:

1 bunch parsley (chop off and discard the woody stems. Tender stems are ok.)
3-5 cloves raw garlic
juice of 1 lemon (buy 2 lemons, you may need more at the end)
pinch of oregano (fresh or dried)
aji molido (or red pepper flakes) to taste
enough olive oil to make a thick paste

Process until smooth, scraping down the side of the processor once or twice.

Add salt and additional lemon juice to your taste. Let stand for at least a few hours for the flavors to meld-- I think she would leave it in the fridge overnight prior to serving. We would just spoon the stuff over grilled meat and it was fantastic.