For sauce, to roast fresh poblano or Anaheim peppers, halve peppers lengthwise; remove stems, seeds, and membranes. Place, cut side down, on a foil-lined baking sheet. Bake in a 425 degree F oven for 15 to 20 minutes or until skins are blistered and dark. Remove from baking sheet; immediately cover tightly with foil. Let stand 30 minutes to steam. With a knife, remove skin from peppers, pulling skin off in strips; discard skin. Coarsely chop roasted peppers; set aside.
Meanwhile, if using fresh tomatillos, place in a large saucepan; add enough water to cover. Bring to boiling. Reduce heat and simmer, covered, for 8 to 10 minutes or until soft; drain.
In a blender container or food processor bowl, place roasted peppers, fresh or canned tomatillos, onion, cilantro, and garlic. Cover and blend or process until almost smooth.
Transfer sauce to a small saucepan. Stir in chicken broth, sugar, salt, and black pepper. Bring to boiling. Reduce heat and simmer, covered, for 10 minutes; stir in sour cream. Set aside.
Wrap tortillas tightly in foil. Heat in a 350 degree F oven about 10 minutes or until heated through.
Meanwhile, for filling, cook onion in margarine or butter until tender. Stir in cream cheese, milk, and cumin. Add chicken or turkey; stir until combined. Spoon about 1/4 cup of the filling on each tortilla near an end; roll up. Place filled tortillas, seam side down, in a 2-quart rectangular baking dish. Top with sauce. Bake, covered, in a 350 degree F oven for 20 to 25 minutes or until heated through. Remove from oven and sprinkle with shredded cheese. Makes 4 servings.
Prepare the sauce as directed through Step 3. Cover and chill for up to 2 days.