A neutral bulk sausage is best, but breakfast or sweet Italian sausage can be used. You’ll need a Dutch oven with at least a 7 1/4-quart capacity. Use small red potatoes, measuring 1 to 2 inches in diameter. Serve this dish with crusty bread and cornichons and Dijon mustard or Herb Sauce (see related content).
1. FOR THE SAUSAGE STUFFING: Adjust oven rack to middle position and heat oven to 300 degrees. Pulse bread in food processor until finely ground, 10 to 15 pulses. Add egg, shallot, garlic, parsley, fennel fronds, mustard, marjoram, and pepper to processor and pulse to combine, 6 to 8 pulses, scraping down sides of bowl as needed. Add sausage and pulse to combine, 3 to 5 pulses, scraping down sides of bowl as needed.
2. Place 18 by 12-inch piece of parchment paper on counter, with longer edge parallel to edge of counter. Place half of stuffing onto lower third of parchment, shaping it into rough 8 by 2-inch rectangle. Roll up sausage in parchment; gently but firmly twist both ends to compact mixture into 6- to 7-inch-long cylinder, approximately 2 inches in diameter. Repeat with second piece of parchment and remaining stuffing.
3. FOR THE CHICKEN: Using kitchen twine, tie together celery, parsley sprigs, marjoram, and bay leaf. Heat oil in large Dutch oven over medium-high heat until just smoking. Pat chicken breasts and leg quarters dry with paper towels, sprinkle with ½ teaspoon salt, and season with pepper. Add chicken, skin side down, and cook without moving it until browned, 4 to 7 minutes. Transfer chicken to large plate. Pour off and discard any fat in pot.
4. Remove Dutch oven from heat and carefully arrange celery bundle, potatoes, carrots, and fennel in even layer over bottom of pot. Sprinkle peppercorns, garlic, and ¼ teaspoon salt over vegetables. Add enough broth so that top ½ inch of vegetables is above surface of liquid. Place leg quarters on top of vegetables in center of pot. Place stuffing cylinders on either side of leg quarters. Arrange breasts on top of leg quarters. Place pot over high heat and bring to simmer. Cover, transfer to oven, and cook until breasts register 160 degrees, 60 to 75 minutes.
5. Transfer chicken and stuffing cylinders to carving board. Using slotted spoon, transfer vegetables to serving platter, discarding celery bundle. Pour broth through fine-mesh strainer into fat separator; discard solids. Let stand for 5 minutes.
6. Unwrap stuffing cylinders and slice into ½-inch-thick disks; transfer slices to platter with vegetables. Remove skin from chicken pieces and discard. Carve breasts from bone and slice into ½-inch-thick pieces. Separate thigh from leg by cutting through joint. Transfer chicken to platter with stuffing and vegetables. Pour ½ cup defatted broth over chicken and stuffing to moisten. Sprinkle with minced parsley. Serve, ladling remaining broth over individual servings.