1. Preheat the oven to 450 degrees.
2. Prep your ingredients: Remove the tomatillos from their husks and rinse. Cut into quarters and place on a cookie sheet. Roughly chop the onions and halve the jalapeño (keep or remove the seeds based on your heat preference) before placing both of them on the cookie sheet.
3. Drizzle a little oil over the vegetables, season with salt, and then place in the oven to lightly char until they are tender.
4. Once everything is cooked through, remove from the oven, and transfer to a blender. Squeeze in the juice from the limes, season with a little more salt, and blend to your desired consistency.
5. Transfer to an airtight container and refrigerate for up to a week.