In a saucepan, heat the oil over medium-low heat. Cook the onion and garlic, stirring frequently, until soft and fragrant. Add the tomatoes, Scotch bonnet, and bay leaf. Simmer for 15 minutes, or until thick like a chutney, stirring occasionally with a wooden spoon and adding a little water if necessary.

Add the tamarind, sugar and fish sauce and season with salt and pepper to taste. Remove the bay leaf and puree in a food processor or blender until smooth. Store in the refrigerator in an airtight container for up to 3 weeks.

Makes about 1 cup.