In a large, heavy skillet over HIGH heat, add the onion, bell pepper, jalapeño, and tomatillos. Let them sizzle and blacken, stirring somewhat frequently. Cook for 4-5 minutes, or until they're starting to slightly soften, and have blackened edges. Remove from the heat.
Blend the blackened veggies, along with the garlic and cilantro, in your blender until smooth. Pour into a saucepan over medium heat, and add the salt, pepper, cumin, veggie broth, and sugar (if using).
Bring the mixture to a simmer, and let cook down for at least 20 minutes — or until you've reached your desired consistency.
Store in an airtight container!
Recipe by The Kitchen Paper at http://c02.ddd.mwp.accessdomain.com/green-enchilada-sauce/