Place the chicken, peppercorns, celery, onion, carrots, garlic, rosemary, crushed pepper, and bacon fat in a large stockpot. Add 2 tablespoons of kosher salt, then pour in enough water to cover the chicken (about 10-14 cups). Bring to a boil, turn the heat down to low and simmer until the chicken is cooked through and tender, about 60 minutes.
Carefully remove the chicken and place it on a large plate. Strain the broth through a strainer into a large bowl. Let the chicken cool and then pick the meat and set it aside. Reserve the vegetables, you can use them later to garnish the bog. Just make sure to pick out the whole peppercorns.
Bring the strained chicken broth to a boil in a large pot with a tight-fitting lid. Add the picked chicken, uncooked rice, sliced sausage, and black pepper. Bring back to a boil and taste for salt. Add enough for the broth to be salted just right.
Reduce heat to low and simmer, covered with the lid for 15-20 minutes, stirring once or twice in the first 5 minutes to prevent the rice from sticking to the bottom. The water should be all gone and the rice should be cooked through. Remove the pot from the heat and let it sit for 10 minutes.
Add the peas, and stir them in.
Serve immediately. You can garnish the bog with hot sauce and the reserved celery and carrots from the broth. Use the leftover broth to moisten the rice if necessary. This is especially helpful when reheating the bog.