Roast Peppers: Broil tomatillos, poblanos, and jalapeños, if using, on a baking sheet on high for 7-10 minutes until the skins are charred. An extra-large baking sheet can hold them all.
Peel Skins: Remove from the oven and quickly add the roasted peppers to a bowl. Cover tightly with foil or plastic wrap and rest for 5 minutes to let the peppers steam and loosen the charred skins. Peel off and discard the charred outer skins. Add the peppers and tomatillos to a blender and set aside.
Sauté Onion and Spices: In a medium saucepan, sauté the chopped onion in 2 Tablespoons of oil until tender, then stir in the garlic, cumin, and oregano for 30 seconds. Add to the blender.
Blend: Add the cilantro and 1 cup broth to the blender and blend everything until smooth. Add the remaining broth and blend until smooth.
1/2 cup fresh cilantro, 4 cups vegetable or chicken broth
Simmer: Transfer the mixture to the saucepan. Season with salt and pepper. Simmer uncovered for 15-20 minutes. Remove from the heat and stir in the lime juice.
1 teaspoon kosher salt, 1/2 teaspoon black pepper, 1 lime
Store in the refrigerator for up to 4-5 days, or freeze for up to 3 months.
Notes
Yield: 7 cups. Serving Size: 1 cup. Make Ahead: Cool completely and store in airtight containers in the refrigerator for up to 4-5 days.Freezing: Pour cooled sauce into freezer bags, lay flat, and freeze for up to 3 months. Thaw overnight in the refrigerator before using.Heat Level: Use both jalapeños with seeds for a medium spice level.