
To char the jalapeño (optional, you can use chopped fresh jalapeño instead*): On a gas stove over medium heat, use heat-safe tongs to hold the jalapeño a couple inches directly over the flame for about 60 to 90 seconds until it’s mostly blackened. Turn it over and repeat the process on the other side. Place it in a small paper bag or in a bowl covered with plastic wrap for about 10 minutes to let it steam (this makes it easy to remove the charred layer). Wipe off the charred outer layer with a clean tea towel, then cut off the green flesh, and slice it into smaller pieces. Add the pieces to your food processor.
To the food processor, add the remaining ingredients (cilantro, sour cream, lime juice, sliced garlic, salt and cumin). Process until the mixture is smooth and light green, with tiny flecks of green from the cilantro. You can use it right away, or refrigerate it for a couple of hours for even better flavor. It will keep well in an airtight container in the refrigerator for up to 5 days.