1. Grind the Porcini mushrooms into dust in a blender or magic bullet. Add Bell’s seasoning, salt and pepper and mix well.
2. Whisk together the softened butter and mayonnaise until smooth. Add the mushroom powder and seasoning mix and stir until well incorporated.
3. Remove the turkey from the packaging and remove any innards from the cavity. Rinse and pat dry.
4. Place the turkey in a large roasting pan. Carefully separate skin from the meat by sliding your hand underneath the skin being careful not to break it.
5. Stuff the mushroom mixture liberally under the skin, and massage the outside of the skin so it’s evenly distributed.
6. Rub any remaining butter mixture on the outside of the skin and make sure the skin is covering the meat and hasn’t pulled away from the top.
7. Sprinkle with additional salt and pepper if desired.
8. Roast upright in a 400°F oven for one hour and 15 minutes, or until a meat thermometer inserted in the thickest part of the breast reads 160° (F.)
9. Let the turkey rest (loosely tented with tinfoil to keep warm) for one hour before carving to prevent the meat from drying out while cutting.

For the gravy:

1. Pour off pan juices after carving and remove most of the fat that floats to the top.
2. Whisk 1/3 cup of sour cream into the defatted pan juices. Taste and season with salt and pepper if necessary before serving.