Preheat oven to 350 degrees F. For chicken filling: In a medium saucepan, combine the water, onion, bouillon granules, garlic and black pepper. Bring to boiling; reduce heat. Cover and simmer about 3 minutes or until onion is tender. Do not drain. In a small bowl, combine sour cream, nonfat dry milk powder and flour; add to onion mixture. Cook and stir until thickened and bubbly. Remove from heat; stir in chicken. Set filling aside.