Preheat oven to 450 degrees.
Remove the husks from the tomatillos. Rinse under warm water well and wipe clean. Cut the tomatillos in half and place into a baking pan with the onions and jalapeno. Roast for 20 minutes until they are tender. Remove and set aside to cool.
Add all ingredients to a food processor and pulse for 1-2 minutes until smooth and creamy. Add a few tablespoons of water if needed until it’s smooth like a salad dressing.
Serve as needed. Keeps in an air tight container for up to 5 days.