Preheat the oven to broil and move the top baking rack to about 6" above the top of the oven. Place husked tomatillos, poblanos, Serrano pepper, and garlic on a baking sheet
. Drizzle with olive oil and broil for about 5 minutes, until vegetables are soft, juicy, and have dark roasting spots on them. Flip tomatillos and peppers over and boil for another 5 minutes.