Preheat oven to 350°. In a large saucepan, saute onion and celery in butter until tender. Add garlic; cook 1 minute longer. Stir in flour, sugar, salt, basil and pepper until blended. Gradually add broth; bring to a boil. Cook and stir 1 minute or until thickened; reduce heat. Add peas and cook 5 minutes, stirring constantly. Stir in chicken. Pour into a greased 13x9-in. baking dish. , For dumplings, in a small bowl, combine baking mix and basil. Stir in milk with a fork until moistened. Drop by tablespoonfuls into mounds over chicken mixture., Bake, uncovered, 30 minutes. Cover and bake 10 minutes longer or until a toothpick inserted in a dumpling comes out clean.