Wondering why the sauce is not vibrantly green? Check out this post: Chimichurri: Debunking The Myths
Here is my personal favorite recipe for chimichurri sauce(main article). You can mix it all together but I prefer to go through a 3-step process while preparing the sauce.
1/2 Cup Olive Oil (For a more mellow flavor use a neutral flavored oil)
1/4 Cup Red Wine Vinegar
1/4 Cup Water
1 small bunch flat leaf-parsley; chopped (should equal about 1/2 cup)
1 medium onion; finely chopped
4 cloves garlic; finely minced
1/2 of a red bell pepper; seeded and finely diced
1 tomato; peeled, seeded, finely chopped
1 Tablespoon dried oregano
1 Tablespoon paprika
1 Teaspoon bay leaf (laurel); very small flakes
1 Tablespoon coarse salt
1 Teaspoon ground black pepper
hot chili flakes to taste (Aji Molido if you can find it)
Make sure all of the fresh ingredients are well washed and clean before preparing.
Add all of the ingredients except the oil and vinegar into a large bowl and toss well to make sure that the salt is spread evenly around the ingredients. Allow to rest for 30 minutes.
Next add the vinegar and water. Mix well. Allow to rest for 30 minutes.
Finally add the oil and mix well. Make sure that the liquids cover the rest of the ingredients. If not add equal parts of oil, water, and vinegar until they are covered at least by a quarter of an inch. Transfer to a non-reactive clean bowl or jar that can be covered. Make sure to cover well. Place in the refrigerator to allow the flavors to blend overnight. For better results prepare at least 2 or 3 days ahead of time. If refrigerated, allow sauce to sit at room temperature for at least an hour or until the oil, if congealed, thins out before serving.
The Boiling Liquid Method: Many in Argentina like to add an extra step to their chimichurri preparation that includes boiling the water and salt together -perhaps the vinegar too- before immediately pouring the mixture over the rest of the ingredients before the oil is added. This helps to tame the pungency of the garlic and parsley thus creating a more mild and smooth chimichurri. This method also works very well if you are short for time and need a well-balanced chimichurri yet do not have the time to let it sit for a day or more before serving. Give it a try.
Parsley-Garlic Chimichurri Recipe