Add the olive oil to a pan over medium high heat and sauté the onion, jalapeño and garlic until tender and slightly charred. Stir in the tomatillos and cook for an additional 2 minutes, until softened.
Transfer the mixture to a blender along with the remaining ingredients and process until your desired consistency is reached.
Use immediately or store in the fridge in an airtight container for up to 7 days, or freeze for up to 5 months. Enjoy!