Mix butter, rosemary, garlic, and lemon zest together and spread mixture under the skin and over the breasts of the chicken. Rub the chicken all over with the lemon half. Both inside and out.
Place chicken in roasting pan lined with onions slices, skin side up. Roast for 45 minutes. Basting occasionally.
Roast Spring Chicken Recipe https://theculinarycure.com/roast-spring-chicken/