Place turkey on ½ baking sheet. Pat dry with paper towels then dry brine with 1 tsp baking powder and 1 tbsp coarse kosher salt per 5 lbs of turkey.
Leave uncovered in fridge for 2-3 days.
On cooking day, set oven rack to lowest position and place a baking stone. Preheat oven to 500°F (260°C). Allow to preheat for at least 45 minutes before adding turkey.
Remove and let come to room temp-ish. Add herb butter mix everywhere. Fold wings back. Tie legs.
Set turkey breast side up in a V-rack.
Transfer turkey on rack directly to baking stone. Immediately close oven and reduce oven temperature to 300°F (150°C).
Roast until turkey is golden brown and deepest part of breast registers 150°F (66°C) on an instant-read thermometer and legs register at least 165°F (74°C), 2.5 to 3 hours total.
Remove from oven and let rest at least 30 minutes before carving.
Carve turkey and serve with gravy.
