Perfect Roast Chicken

Ingredients

• 1 6-pound roasting chicken
• 2 tablespoons unsalted butter
• Salt and freshly ground black pepper
• 2 medium onions, peeled and sliced crosswise ½ inch thick
• 2 lemons
• 3 large cloves garlic, peeled
• 4 sprigs fresh thyme
• 1 cup Homemade Chicken Stock , or canned low-sodium chicken broth, skimmed of fat