Wash jalapeños under cold water, remove stems, slice open and remove seeds for milder sauce. Peel and chop red onion.

In a medium pot, combine jalapeños and red onion with enough water to cover. Bring to a rolling boil and reduce heat, letting it boil for about 10-15 minutes.

Carefully remove from heat and strain the vegetables, saving about half a cup of the cooking liquid.

Transfer drained vegetables to a food processor. Add garlic, oil, and a pinch of salt. Blend for 4-5 minutes until smooth.

Check sauce consistency; if too thick, add reserved cooking liquid and blend until desired consistency is reached.

Serve immediately or refrigerate for at least 30 minutes to deepen flavors. Store in an airtight container.