Line 2 baking sheets with tin foil or silicone mat for easy clean up.
Husk and rough chop the tomatillos. Rough chop the jalapeno and poblano peppers, include the seeds for a spicier version or de-seed to make the salsa verde more mild. Rough chop the garlic and onion.
Place all the chopped vegetables in a large mixing bowl. Drizzle with 1/4 cup olive oil. Stir in 2 Tbsp cumin, salt and pepper. Add olive oil and cumin as needed to fully coat all vegetables. Pour out on to prepared baking sheets, spreading evenly.
Broil on top rack 5 to 10 minutes, stirring at the 5 minute mark to check on the vegetables. Broil until starting to soften and blacken a little. Some charring will add to the flavor.
Remove from oven and drain both baking sheets into a sauté pan, including all accumulated juices.
Bring vegetables to a boil, then reduce heat and simmer approximately 30-45 minutes. Season with salt and pepper to taste.
Remove from heat. Use an immersion blender to puree ingredients. Sauce should be rich and thick. Serve warm over tacos or meat of your choice. Sauce can also be chilled for a dip.