Prep: 1 hour
1. Remove offal and cut the rabbit into quarters and separate the loins, removing the rib bones. Set the offal and quarter pieces aside.
2. Season the loins with salt and roll tightly lengthwise, beginning on the thickest side, rolling to the thin end. Rest rolled loins on the seam and store in the refrigerator until time to cook.
3. Using a heavy Dutch oven or cast-iron pot with a fitted lid, heat a splash of oil over medium-high heat. Season rabbit quarters liberally with salt and pepper. Brown hind and forequarters in the oil, on both sides, until golden. Remove from pot and set aside.
4. Preheat oven to 225°F. Add bacon lardons to the pot and render until just beginning to crisp. Add onion, carrots, and turnip or celery root, and sauté in rendered fat until just tender. Add garlic, cook for another 2 minutes. Add tomatoes, cook 1 minute, then deglaze with red wine, making sure to scrape all the brown bits off the bottom. Cook for another minute before adding back in browned rabbit quarters and enough stock to barely cover. Stir to incorporate. Nestle rosemary sprigs and 1 cup sliced mushrooms in the liquid. When mixture comes to a slight simmer, cover and transfer to oven and braise for 45 minutes to 1 hour.
5. Remove from oven and check rabbit for doneness by inserting a skewer or fork into the flesh. When perfectly cooked, the skewer should go in easily and have minimal resistance when removing.
6. Heat a cast-iron or non-stick pan over medium-high heat. Add a small amount of oil and gently lay rolled loins in the pan, seam-side down. Cook for 2 minutes before turning and cooking evenly on all sides, about 8 minutes total. When halfway cooked, add remaining 1 cup of mushrooms to the pan, and sauté with the loins. When loins are just about done, add offal and toss until just cooked. Remove loins and offal to a cutting board and slice the loins into small medallion rounds and offal into bite-size pieces. Add mushrooms to skillet and cook, stirring occasionally, until nicely golden brown, about 8 minutes.
7. Pile the mashed potatoes on the bottom of a large rimmed platter. Scoop cacciatore over the potatoes, and layer the large rabbit pieces on top. Sprinkle with sliced rabbit medallions and offal and top with sautéed mushrooms and chopped parsley. Serve immediately.