Season and roast the turkey. Heat the oven to 325°F. Pat the turkey dry. Mix the softened butter with the chopped sage, salt, and pepper. Rub most of it under the breast skin and the rest over the outside. Set the turkey breast-side up on a rack in a roasting pan and roast unstuffed. Start checking the temperature after about 2½ hours.
Make the glaze. While the turkey roasts, boil the cider in a small saucepan until reduced to about ¾ cup. Turn off the heat and whisk in the Dijon, vinegar, and butter. Pour about ⅓ cup into a separate bowl for brushing and reserve the rest for serving.
Glaze and rest. Brush the turkey during the final 20–30 minutes of roasting. If the skin gets too dark, loosely tent it with foil. The turkey is done when an instant-read thermometer registers 165°F in the thickest part of the breast and the innermost parts of the thigh and wing, without touching bone. Transfer to a carving board and rest loosely tented for about 30 minutes.
Roast the pears and shallots. While the turkey rests, raise the oven to 425°F. Toss the shallots with half the olive oil and half the salt, then roast cut-side down on a rimmed baking sheet for 10 minutes. Toss the pears with the remaining oil and salt, add them to the sheet, and roast for another 12–18 minutes, until the pears are golden and the shallots are tender.
Crisp the sage and assemble. Heat the neutral oil in a small skillet over medium heat. Fry the sage leaves in batches for about 10–20 seconds, then drain on a paper towel. Fan the sliced breast across a warm platter, tuck the drumsticks and carved thigh meat alongside, and arrange the pears and shallots around the edges. Scatter the sage over the top and serve the reserved cider sauce on the side.