In a sauce pot over high heat, bring the water to a boil, then add in the jalapeño peppers, minced onion, and garlic. Turn the heat to low and allow the ingredients to simmer for 10 to 12 minutes (until the jalapeños have softened).
Strain the ingredients from the water, then keep the water in a bowl to the side.
In the same sauce pot, add the jalapeño pepper/garlic/onion mix, tomato paste, light brown sugar, and cumin. Process the ingredients using a food processor until smooth.
Add water from the reserved water as needed to get the right consistency. Also add additional sugar to taste to get your preferred sweetness.
Use immediately, or refrigerate in an airtight container for future use (up to two weeks). Note the sauce will be hotter the longer it sits.