Preheat oven to 400°.
Combine first 5 ingredients in a small bowl; mash to a paste consistency.
Remove and discard giblets and neck from chicken. Rinse chicken with cold water; pat dry. Trim excess fat. Starting at neck cavity, loosen skin from breast and drumsticks by inserting fingers, gently pushing between skin and meat.
Rub seasoning mixture under loosened skin. Place onion in body cavity. Lift wing tips up and over back; tuck under chicken. Tie legs together with string.
Place chicken, breast side up, on a broiler pan coated with cooking spray. Insert a meat thermometer into breast, making sure not to touch bone. Bake at 400° for 1 hour and 20 minutes or until thermometer registers 180°. Remove chicken from pan. Cover with foil, and let stand 10 minutes. Discard skin.
Place a zip-top plastic bag inside a 2-cup glass measure. Pour pan drippings into bag; let stand 5 minutes (the fat will rise to the top). Seal bag; carefully snip off 1 bottom corner of bag. Drain drippings into pan, stopping before fat layer reaches opening; discard fat.
Place pan over medium-high heat. Stir in wine, scraping pan to loosen browned bits. Add broth; bring to a boil. Cook until reduced to 2/3 cup (about 3 minutes). Remove from heat; add butter, stirring with a whisk until well blended. Serve sauce with chicken.