Slice the stems off the fresh jalapeños and coarsely chop the red onion. In a medium pot, combine the jalapeños with the chopped onion. Add enough water to cover the vegetables completely. Bring this mixture to a vigorous boil over medium-high heat.

Once boiling, reduce the heat to low and let the vegetables simmer for about 15 minutes until the jalapeños are soft but not mushy.

Carefully strain the jalapeños and onions using a colander, reserving some of the cooking liquid. Set aside to cool slightly.

Transfer the softened jalapeños, onion, and garlic into a food processor. Add the neutral oil and a pinch of salt, then blend for about 4-5 minutes until smooth.

If a thinner sauce is desired, gradually mix in the reserved cooking liquid and blend thoroughly until the desired thickness is achieved.

Taste the sauce and adjust seasoning by adding more salt as needed.

Refrigerate the sauce for a few hours to allow flavors to meld beautifully.