Remove thawed chicken from the refrigerator. and let it stand at room temperature for half an hour.
Empty the cavity of the giblets. Place giblets in a small pan with a cup of water, and your favorite seasonings to make a bit of broth to add to the gravy later, if desired.
Preheat the oven to 425 degrees.
Slice the onions, then place in two rows on the bottom of the roasting pan.
Lay the chicken on the bed of onions, breast side up, tucking the wing tips of the chicken under. Stuff the chicken cavity with the rosemary, lemon, and garlic cloves.
Bring the legs of the chicken forward, then tie together with carpet thread or twine.
Spread the butter over the chicken, then sprinkle with salt and pepper.
Roast for one and a half hours. If you have a meat thermometer, you could check the temperature in the deepest part of the thigh. The thermometer should read somewhere between 165 to 175 degrees.
Remove the chicken and onions from the pan. Discard the onions. Strain the pan juices and return them to the pan for making the gravy. Use your favorite method to thicken the gravy. I like to mix one-fourth cup of flour with one cup of the broth from the pan of giblets. Add this to the pan, heating over medium-high heat for about 4 minutes. When the mixture comes to a boil, it should thicken up.
Serve the roasted lemon rosemary chicken (also known as baked lemon rosemary chicken) on a platter. Garnish with additional rosemary stems and slices of dried lemon for a decorative touch, if you have them.