Here's the update as I cooked two 18# turkeys as a trial run for Thanksgiving.
I'm thinking I should be doing this for a living - oh wait, I already am!
Best. Turkeys. Ever. Ever. Anywhere. Ever.
I did all this research a couple weeks ago (it's what first brought me to ChefTalk) and the general method out there was roasting the spatchcocked turkey in the oven, with a variation of doing it over stuffing (an idea I love - Thanks, Julia). The other professional suggestion out there was breaking down the turkeys completely into white and dark meat and cooking them separately. I wanted to keep the integrity of the turkeys intact as much as possible knowing that the juices would stay in the bird much better that way, and I simply wanted to use the method I employ for roasting whole chickens and apply it to turkeys.
Here's what I did:
I cut out the backbones, made a gash in the top of the keel bone with my knife and pressed down to flatten the turkey further, and did a general prep on the birds including a token salt and pepper rub inside.
I rubbed a very light coating of oil on the skin and laid each bird down in very hot GI Pan covers that I use for searing and large-batch pan-frying. I used no oil in the pans themselves. Each pan covered 2 burners so I had to be aware of too-hot spots. Searing took about 10-12 minutes and rendered quite a bit of fat and left the skin crispy and looking amazing! Using 2 pairs of heavy-duty tongs (I own no others) I transferred the turkeys to a sheetpan, skin side up. Between the processing of the birds, the spatchcocking process and the searing, there was some disconnect at the point where the thigh meets the bottom part of the breasts on 1 of the birds so I used the other bird and a couple pieces of bunched-up foil to keep the thighs against that thinnest and most-easily overcooked part of the bird. I put them inside my CresCor Roast-and-Hold oven at 310F for 1 1/2 hours and then had the hold temp dropping down to 140. I was too involved with something else when the hour-and-half was up so pulled them out about 20 minutes later and the temp on the breast was in the mid-150s, thigh was over 170. They looked and smelled perfect. My intent was to have them just a bit undercooked so I could use this method for Thanksgiving, getting all the work done on Wednesday and finishing them up on Thanksgiving day. When I broke them down an hour later they couldn't have been more perfectly cooked. The legs and thighs were completely cooked and the breasts were just this side of done - the thickest internal parts of the breast had that slight shading of pink, but the meat had the proper look and texture. Perfectly cooked, and able to handle a gentle reheating with some stock under it. The 2 turkeys yielded about 3 cups of delicious au jus (after fat removal).
I feel great going into my first Thanksgiving under my new catering business - these turkeys are going to blow people away!