Place tomatillos, onion, garlic cloves, and jalapenos on a baking sheet. Drizzle with oil and toss to coat. Roast for about 20 minutes, or until the tomatillos are soft and slightly charred. If your veggies are soft but not charred, place under the broiler for 2-4 minutes - keep an eye on them. Remove from oven when your desired charring is achieved.
1 lb tomatillos, husked and rinsed, 1 medium onion, quartered, 1 cloves garlic, 2 jalapeno, stemmed, seeds removed for less heat, 1 tbsp oil