Place 1 lemon half and onion half into chicken cavity. Squeeze remaining lemon half into chicken cavity.
Stir together butter, garlic, and thyme. Starting at neck cavity, loosen skin from breast and drumsticks by inserting fingers and gently pushing between skin and meat. (Do not totally detach skin.) Rub half of butter mixture evenly under skin.
Tie ends of legs together with string; tuck wingtips under. Spread remaining half of butter mixture over chicken. Sprinkle evenly with salt and pepper. Place chicken, breast side up, on a lightly greased rack in a lightly greased shallow roasting pan.
Bake at 450° for 30 minutes.
Reduce heat to 400°, and bake for 55 to 60 minutes or until meat thermometer inserted into thigh registers 180°. Cover loosely with aluminum foil to prevent excessive browning, if necessary. Remove to a serving platter, reserving drippings in pan. Cover with foil, and let stand 10 minutes before slicing.
Add broth to reserved drippings in pan, stirring to loosen browned bits from bottom.
Whisk together pan drippings mixture, wine, and flour in a small saucepan. Cook, stirring often, over medium heat 5 minutes or until thickened. Serve with chicken.
Chipotle Roasted Chicken: Substitute 1 canned chipotle pepper, chopped, and 1/4 cup adobo sauce from can for 3 garlic cloves and 2 teaspoons chopped fresh thyme. Sprinkle chicken with 1 teaspoon ground cumin and with 1 teaspoon each salt and pepper. Proceed as directed.