Preheat oven to 500 degrees. Very liberally season all sides of the roast with salt and pepper. Place roast in a large roasting pan. Cook at 500 for 15 minutes to establish a nice crust on the outside of the roast. Reduce heat to 325 and cook 13-15 minutes/lb for a rare roast. Use a meat thermometer to check doneness. A rare roast will register 115-120 degrees. Remove from oven and let rest for AT LEAST 15 minutes. Carve roast in to individual chops per serving.
Cook potatoes in heavily salted boiling water. Potatoes should be cooked but still slightly firm. In a large bowl, combine potatoes and parsley. Using a potato masher, break down potatoes. Add heavy cream and truffle butter. Continue to mash. Do not over mash or potatoes will become gummy. Some lumps are ok. Season with salt and pepper.
Blanch Brussels in heavily salted boiling water. Immediately transfer to ice water to stop cooking process. In a large sauté pan, cook bacon until it begins to brown. Add shallots continue to cook until brown. Add blanched Brussels. Continue to cook until Brussels Sprout begin to get nice brown color on all sides. Finish with lemon zest, salt, and pepper.