10 ounces pearl onions or 3 large onions
1 4-5 pound whole chicken
1 tablespoon olive oil
4 tablespoons margarine at room temperature, divided
10 ounces cremini or white mushrooms, sliced
1 bag frozen asparagus
Kosher salt to taste
1/4 cup dry white wine
Preheat oven to 425 degrees F.
Rinse and pat chicken dry. Rub 2 tablespoons softened margarine into skin over entire chicken. Season chicken inside and out with salt and pepper. Cut the lemon in half and put one half in cavity and squeeze remaining half over chicken.
Roast chicken in middle of oven 30 minutes. Baste chicken with accumulated juices, then continue to roast, basting about every 10 minutes, 30 minutes more. Scatter onions around chicken and continue to roast, turning onions and basting every 10 minutes, until chicken is golden and a thermometer inserted into fleshy part of a thigh registers 180 degrees F (juices will run clear), 25 minutes more.
Transfer roast chicken to a platter, then discard string and cover chicken loosely with foil. Transfer onions to a small bowl and set aside. Pour pan juices into a small bowl (do not clean roasting pan). Skim and discard fat from juices.
Place roasting pan on your stovetop over high heat. Add wine and deglaze by boiling, stirring and scraping up brown bits, until reduced to about 2 tablespoons. Add pan juices from bowl, and mushrooms; then boil until liquid is reduced to about 1/3 cup.
Add remaining 2 tablespoons margarine and add to the pan along with onions and asparagus. Cook over moderately high heat, shaking pan, until butter is just incorporated and vegetables are glazed. Season vegetables with salt and pepper and spoon them around chicken. Serve immediately.