Turkey will take about 1 1/2 times to twice as long to cook from frozen.
Preheat oven to 325.
Remove wrapping from turkey and place breast down on broiling pan.
Place in oven for 3 1/2 hours.
Remove from oven and see if bag with liver, gizard and heart can be removed from the neck area. If not return to oven and continue checking every 15 minutes. If the bag is plastic, do not let it begin to melt or it will ruin turkey.
Flip turkey breast side up and return to oven for another 30 minutes.
Remove from oven and see if neck can be removed from the body cavity from between the legs. If not return to oven and continue checking every 15 minutes.
Peel outer skin off onion and place in body cavity along with garlic.
Rub body down with butter and season with salt pepper and poultry seasoning.
Return to oven to finish cooking. Check for temperature in thigh of at least 175 and in breast of at least 160. Baste turkey with juices every time you check temperature.
When temperature is reached, remove from oven and tent in aluminum foil for 30 minutes to allow turkey to rest before carving.