Remove the backbone: Place the turkey breast-side down on a cutting board. Using sharp poultry shears, cut closely along one side of the backbone from the tail to the neck.Turn the turkey around and repeat on the other side of the backbone to cut it out completely. Save the backbone for making turkey stock.
Flip and flatten the turkey: Turn the turkey over so the breast side is facing up. Using your palms, press down firmly on the breastbone to flatten the turkey. You may need to apply pressure a few times to crack the breastbone.If you have trouble breaking the breastbone, use a sharp knife to make a small incision along the top of the breastbone before pressing down.Continue pressing until the turkey is flattened evenly. The turkey is now ready for seasoning and roasting or smoking.
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Notes
After spatchcocking the turkey, use a sharp knife to trim off any loose neck skin that may hang down. This excess skin can potentially burn when cooking the turkey.
I highly recommend dry brining the turkey for 24 hours prior to cooking it for best results.