Place your oven rack at the lowest position in the oven. Preheat the oven to 400. Remove defrosted turkey from the packaging and put it on a large baking sheet to prep.

To prepare the turkey, remove the neck from the inside the large cavity of the turkey, then remove the bag of giblets from the back end cavity of the turkey.  If you aren't going to use them to make gravy, (I don't), you can discard.  Tuck the excess flap of skin that is on the back end of the turkey cavity back in.  Fold the back wings underneath the bird.  Your legs should already be tied together but if not, you can tie them together at the tips with baking string. Set aside.

Place a turkey roasting bag in a turkey roasting pan on it's side on top of the rack and sprinkle 1 Tbsp flour in the bottom of the turkey bag. Set the roasting pan aside.

To make the turkey butter, in a small mixing bowl, add the room temperature butter, salt, tarragon, thyme, sage, rosemary, lemon zest and minced garlic.  Use a spatula to combine it all until it's fully incorporated.

With your fingers or a rounded edge of a spoon handle, gently loosen the skin that is over the breasts so you can slide butter under the skin. Push some of the butter under the skin as far back as you can get it, then gently pull the skin back over the breast as far as it will go without ripping.

Have someone hold the bag open for you while you slide the turkey in to the bag with the large open cavity facing towards the front of the open bag.

Place the chunks of onion and lemon in to the the large open cavity then wash your hands extremely well!

Use the bag tie to close the bag and make six small slits in the the top of the bag with a knife.

Place the roasting pan in the oven, making sure that the bag is not touching any part of the oven.  Bake at 400 for 30 minutes, then reduce the heat to 350 and cook an additional 2 to 2-1/2 hours (for a total of 2-1/2 to 3 hours in the oven for the 20-24 pound turkey.)

For your turkey to be cooked properly You will want the breast and thighs to register at least 160 with an instant read thermometer before it comes out of the oven. (It will continue to climb in temp while it is resting to hit the 165.)  Start checking after the lowest time of the range listed by pound.  For the 20-24 pound turkey you will start checking after 2 hours at 350.  You can stick the thermometer right through the bag into the meat, just don't touch the bones with it when taking the temp. If the meat is not registering at 160-165 in BOTH places, then place it back in the oven for 10-15 minutes at a time until the right temp is reached.

Once the turkey is ready, remove the turkey from the oven, then let rest for 30 minutes before carving to let the juices redistribute.

Carve off the meat, drizzle with a bit of the buttery drippings and then serve!