Step 1: Wash and thoroughly dry the fresh flat-leaf Italian parsley. Finely chop the parsley and set aside. Ensure it is very dry to prevent a watery sauce.
Step 2: Peel and finely mince the garlic cloves. Finely dice the red onion, if using. Finely chop the fresh oregano leaves, or measure out dried oregano.
Step 3: In a medium bowl, combine the finely chopped parsley, minced garlic, diced red onion (if using), and chopped oregano. Add the red pepper flakes, sea salt, and freshly ground black pepper.
Step 4: Pour in the red wine vinegar and stir well to combine all the ingredients. Let it sit for 1-2 minutes to allow the herbs and garlic to start macerating in the vinegar.
Step 5: Slowly drizzle in the extra virgin olive oil while continuously stirring with a spoon or whisk. Continue stirring until all ingredients are well incorporated and the sauce is emulsified.
Step 6: Taste the chimichurri recipe and adjust seasonings as needed. You might want more salt, pepper, or red pepper flakes.
Step 7: For best results, cover the bowl and let the chimichurri rest at room temperature for at least 30 minutes, or ideally, refrigerate for 2-4 hours before serving. This resting period allows the flavors to meld beautifully. Bring to near room temperature before serving for optimal flavor and consistency.