Preheat the oven to 400 degrees F.
Place the tomatillos, jalapenos and garlic on a rimmed baking sheet. Toss with olive oil and season with salt and pepper. Roast until turning brown, 20 to 30 minutes. Remove the garlic cloves from their papery skins and put all the roasted ingredients in a blender, adding in any roasting juices, as well as the cilantro. Puree and season with salt and pepper if needed.