Combine ingredients:
In a food processor or blender, add parsley, cilantro (if using), garlic, red pepper flakes, salt, and black pepper. Pulse until everything is finely chopped.
Add liquid.
With the machine running, slowly add the olive oil, red wine vinegar, and lemon juice, mixing well.
Taste and adjust.
Taste the sauce and adjust seasonings as needed.
Store:
Pour into glasses and let sit for at least 30 minutes to allow flavors to meld. Store in the refrigerator for up to 1 week.
Appetizers galore!
Use this chimichurri sauce as a marinade or as a topping for grilled steak, chicken, or vegetables.