Preheat oven to 180°F.
Remove excess fat from the bottom and top of the goose, then prick the skin all over with a sharp knife. Season the goose all over with salt. Stuff the cavity of the goose with a quarter of the leeks, carrots, onions, celery and garlic.
Place the goose in a very large Dutch Oven or pot. Add the remaining leeks, carrots, onions, celery and garlic around the goose along with the peppercorns and bay leaves. Stir together 2 cups of the white wine and tomato paste in a measuring cup and pour into the pot. Add enough water to the pot to cover the goose halfway.
Set the pot on the stovetop, and heat over medium-high heat with the lid on. Bring the liquid to a simmer, then remove the lid and place the pot in the preheated oven. Cook until the goose is cooked through and beginning to brown on top, about 2 1/2 to 3 hours.
Remove the pot from the oven and remove the goose from the pot. Refrigerate the goose overnight, separate from the broth. Remove the aromatics from the broth in the pot and place the pot in the refrigerator overnight too. Alternatively, you can strain the broth into another container and then place in the refrigerator.
The next day, skim the fat off the top of the stock and reserve. Strain the stock through cheesecloth and set aside.
Preheat oven to 450°F.
Place the pears, parsnips, sweet potatoes, rosemary and thyme in the Dutch Oven and season with salt and pepper. Add 1 tablespoon of the reserved goose fat and toss to coat the vegetables. Coat the outside of the goose with a couple of tablespoons of the reserved goose fat and season with salt and the Chinese Five Spice Powder. Place the goose in the pot on top of the vegetables.
Place the pot in the preheated oven and cook until the goose is hot and crispy, and the vegetables are tender, about 45 minutes to 1 hour. Remove from the oven. Place the duck on a cutting board and let rest 15 minutes.
Meanwhile remove the vegetables and place in a dish to keep warm. Remove any fat from the pot, leaving a couple of tablespoons. Place the pot over medium heat. Add the shallots and sauté until softened and beginning to brown, about 5 minutes. Add the remaining 1 cup white wine and stir to scrape up the bits in the pot. Let simmer until reduced slightly. Add the jelly and mustard and whisk to combine. Add 2 cups of the reserved stock and bring to a simmer. Season to taste with salt and pepper and keep warm.
Carve the duck and place on a platter. Serve alongside the roasted vegetables and pan sauce.