Preheat oven to 350 degrees. Line a rimmed baking sheet or pan with parchment paper and set aside.
NOTE: If you purchase frozen turkey legs and thighs, they must be fully thawed and at room temperature before attempting this recipe.
Pat the turkey legs and thighs completely dry with paper towels. Set them aside.
Combine the butter, summer savoury, thyme leaves, rosemary, onion flakes, salt, and pepper. Whisk it all together until the herbs and seasonings are well incorporated into the butter.
Use about two tablespoons of the butter mixture to fully massage each piece of turkey with. This is messy, but the best way to do it is to pick up the turkey leg or thigh in one hand, scoop a mound of butter into your other hand, and massage the butter completely around the turkey. It should be coated thick.
Transfer the butter-slathered turkey to the baking sheet, being careful to not let the pieces overlap and not to touch the side of the baking pan.
Cover with foil, and bake for one hour.
Remove from oven, baste each piece of turkey with the melted butter and turkey juices in the pan. Cover and return to the oven. Repeat this every fifteen minutes for the next hour. Leave the foil off the last 15 minutes.
Transfer the turkey to a serving platter, spoon over some of the butter and herbs. Garnish with more rosemary, summer savoury, and thyme if you wish, and serve.