Pat the duck legs dry with paper towels and season them generously with salt and pepper. Heat the olive oil in a large Dutch oven over medium heat, then sear the duck legs skin-side down for 8 to 10 minutes until the skin is deeply golden brown and crispy. Flip and cook for another 3 to 4 minutes, then transfer the duck to a plate and discard all but 2 tablespoons of the rendered fat from the pot.

Add the onion, carrot, and celery to the same pot with the reserved duck fat. Cook over medium heat for 6 to 8 minutes, stirring occasionally, until the vegetables are soft and translucent. Stir in the minced garlic and cook for 1 minute more until fragrant.

Pour in the red wine, scraping up any browned bits from the bottom of the pot with a wooden spoon. Bring to a simmer and let the liquid reduce by half, which should take about 5 minutes.

Stir in the crushed tomatoes, chicken stock, rosemary sprigs, and orange peel. Return the duck legs to the pot, submerge them in the liquid, and bring the mixture to a boil. Reduce the heat to low, cover with a tight-fitting lid, and simmer gently for 75 to 90 minutes until the duck meat is falling-off-the-bone tender.

Carefully transfer the duck legs to a cutting board and discard the rosemary sprigs and orange peel from the sauce. Remove and discard the skin and bones, then use two forks to shred the tender duck meat. Stir the shredded meat back into the simmering sauce and cook uncovered for 10 minutes to thicken.

While the sauce finishes thickening, cook the pappardelle in a large pot of salted boiling water according to package directions until al dente. Drain the pasta and toss it directly into the Dutch oven with the hot duck ragu, serving immediately with grated Parmesan cheese and fresh black pepper.