Preheat oven to 350 degrees. Spread bread cubes on a rimmed baking sheet and bake until crisped but not golden, about 10 minutes. Let cool. In a 14-inch straight-sided skillet (or 2 large skillets), melt butter over medium-high heat. Add onions, leeks, celery, fennel, and pears; season with salt and pepper. Cook, stirring occasionally, until vegetables and pears are softened and start to turn golden, about 15 minutes. Stir in rosemary and sage.

Meanwhile, cook sausage in a skillet over medium heat, stirring occasionally and breaking into large crumbles, until browned and cooked through, about 10 minutes. Drain on paper towels. Stir into vegetable mixture, then transfer to a large bowl. Add bread cubes and toss well. Drizzle stock over mixture, add eggs and parsley, and toss to combine well. Season with 2 teaspoons salt and 1/2 teaspoon pepper. Use 10 cups stuffing to fill bird; place remainder in a buttered 8-inch-square baking dish. After turkey is out of oven, bake at 350 degrees until heated through and top is browned, 40 to 45 minutes.