Start by chopping the red onion, jalapeños, and cilantro. Make sure to wash the cilantro thoroughly to remove any dirt.
In your food processor, add the chopped red onion, jalapeños, olive oil, mayonnaise, white vinegar, yellow mustard, kosher salt, black pepper, and the crushed garlic cloves.
Secure the lid on your food processor and blend the ingredients until you achieve a smooth and creamy consistency. You may need to stop and scrape down the sides to ensure everything is well combined.
Now, add the chopped cilantro to the mixture. Pulse a few times until the cilantro is finely chopped and incorporated, but be careful not to over-blend; you want some texture in your sauce.
Once blended, taste your sauce. Adjust the seasoning if needed by adding more salt, pepper, or vinegar to suit your preference.
Transfer your Peruvian Green Sauce to a serving bowl, or store it in an airtight container in the refrigerator for later use. It’s best served fresh, but it will also keep well for a week.