Page 72 - Turkey Book from Meathead

1) When you open up the bird by removing the backbone and lay it flat, you can brown the cavity. Brown is beautiful. It has more flavor than the pale unappetizing cavity of a whole Norman Rockwell bird. Browning is a well-known process called the Maillard reaction. Spatchcocking also allows you to season and brown both sides evenly.
2) Because hot air circulates on all sides, a spatchcocked bird cooks faster and loses less moisture, and when it comes to turkey breasts, moisture is critical. Because heat enters the meat from two sides the top side doesn't dry out as much.
On a day when the air temp was 65°F we cooked a spatchcocked 18 pounder in less than 90 minutes on a Weber Kettle at about 325°F. Your cooking time will depend a lot on