Roast whole poblano and jalapeño peppers, without oil, under broiler or on grill until skin is burnt and peeling off. Place peppers in a brown paper bag or in a bowl covered with plastic wrap. Once cool, remove skins and set aside. Cook onions and garlic in olive oil over low heat until onions are translucent. Add tomatoes and enchilada seasoning, bring to a simmer and cook for 5 min. Place poblano, jalapeño and tomato sauce in a blender or food processor and blend until smooth. Fold in sour cream and salt to taste. (More sour cream brings down the heat a bit.)
This sauce is excellent for enchiladas or on top of burritos, tacos or shredded chicken. Recipe yields perfect amount for 8 enchiladas.