I plan on dry brining the turkey before spatchcocking. I was planning on roasting at 450 degrees for 30 minutes and turning the heat down to 400 degrees for the rest of the time.
AntoniaJames does her spatchcocked turkey exactly like you're planning (450° F to start, then down to 400° F after 30 minutes, read her recipe here: https://food52.com/recipes...), and she's found that after you decrease the temperature, you'll need to roast for about 10 minutes per pound, total. She also recommends covering the breast after an hour with heavy foil (or after an hour and a half for a larger bird) and starting to check the internal temperature of the bird about halfway through cooking—the turkey is done when the thigh's internal temperature is 165° F.
Thanks! 10 minutes per pound seems a little long for a spatchcocked bird, but since I'm not an expert I'll plan accordingly. Thanks for the quick reply.
Jack, you're right. I tested a smaller turkey for that recipe and had to rely on someone else (it happened to Melissa Clark of the New York Times) for scaling it up to a larger bird. Based on the comments in the recipe, my original instructions are off, recommending a much longer time than is necessary. You should start checking at 2 hours and, as noted, put foil on the breast when it starts looking very dark. I see in the comments to my recipe that someone with a 25 pound bird found that theirs was done in 2 1/4 hour, so you may want to check after 1 hour and 50 minutes. Ovens vary widely, because of their own heating and insulating properties, and then there's the question of the oven being opened and shut, which tends to happen a lot on Thanksgiving day. Key though is to check, starting early, to prevent overcooking. ;o) P.S. I'm going to ask the editors to revise the instructions in my recipe to reflect this additional information. I cannot do it because it was contest finalist and therefore is locked down.