To the bowl of a food processor, add the shallot, garlic, Thai chili, jalapeño, cilantro, and lime juice. Blend until smooth but slightly textured.
Transfer to a bowl and stir in the fish sauce and brown sugar. Taste and adjust sweetness or saltiness as needed.
Notes
Storage: keep in an airtight jar in the fridge for up to 2 weeks, the fish sauce and lime juice help preserve it. Give it a stir before using since it can settle.