Spatchcocking is the process of cutting out the backbone of poultry and flattening the bird. This allows the bird to cook more evenly, so all the meat is moist and tender while the skin is crispy and brown. It also makes for easily meat carving ahead, so the platter is all set when brought to the table.
Normally, I (Jim) cook my turkeys low and slow; An hour on the grill, then four hours in the oven at 275 degrees, increasing the temperature only for the last hour to crisp up the skin. It's usually at 5-6 hour process.
We've used this trick successfully with chickens to cook them in 45 minutes. The result is delightfully moist meat and crispy skin! We cooked our first spachcocked turkey for exactly 90 minutes for a 15 lb bird to come to 158 degrees. We took it out and let it rest covered with foil and dish towels. Internal temperature hit 165 degrees within 15 minutes.
Thaw the poultry if necessary -- in the fridge 1 day/5 lb of bird, or in a tub of water in the fridge 12 hours/1 lb.
Preheat the oven to 450 degrees. Remove the giblets and reserve for gravy. Wash the bird and pat dry. Lay breast side down. Using a sharp knife and/or scissors, saw and cut along each side of the spine to remove it. Take your time and be careful not to cut yourself. This is the hardest part! Reserve the back bone with the giblets.
While the bird is still breast-side down, score the inside of the sternum. Turn the bird over, breast side up. Press firmly on the breast until the breastbone cracks and the bird flattens out.
Rub the bird with olive oil, and sprinkle with salt and herbs. Place the breast side up on wire racks on a baking sheet (with sides to hold the drippings). Insert a meat thermometer into the breast. Place the bird in the oven so you're able to visualize the thermometer reading without opening the oven door if possible. Check the internal temp in a half hour. Refrain from opening the oven often, but you may want to move the thermometer occasionally to confirm readings.
When the temperature reaches 155 -160 degrees, remove the bird from the oven. Leave the thermometer inserted and cover with foil. Let rest for 30 minutes. The temp should rise to 165 degrees while resting. If the temp under-shoots, you risk under-cooked poultry. If the temp rises past 170, you risk dry meat.
After 30-60 minutes you can carve the bird and arrange artistically (or not!) on a platter.