Let chicken and butter stand at room temperature for 30 minutes
Preheat oven to 425°F
Rinse chicken inside and out under cold water and pat dry with a paper towel
Place the palm of your hand on top of lemon and, pressing down, roll lemon back and forth several times (This softens the lemon and allows the juice to flow more freely)
Pierce entire surface of lemon with a fork
Using the side of a large knife, gently press on garlic cloves to open slightly
Insert garlic cloves, thyme sprigs, and lemon into cavity of the chicken
Cover the bottom of your roasting pan with onion slices and place chicken in pan on onion slices
Spread the softened butter over entire surface of chicken, and sprinkle liberally with salt and pepper
Place in the oven, and roast until skin is deep golden brown and crisp, and the juices run clear when pierced, about 1 1/2 hours
The chicken is done when the temperature in the thigh reads 190°F on an instant read thermometer
Remove chicken from oven and let chicken stand 10 to 15 minutes so the juices settle
Remove and discard garlic, thyme, and lemon and carve
