Remove stems from chilies, cut into chunks, and place in a blender with garlic, vinegar, sugar, oil, and salt. Blend for about 30 seconds until a paste forms, adding a splash of water if needed.

Transfer paste to a saucepan, add the 1/4 cup water, and simmer over low heat for 10 minutes, stirring often, until the sauce deepens in color and thickens slightly.

Remove from heat and pour into a clean jar. Cool to room temperature with the lid off, then seal and refrigerate.