Special equipment: 1 package cheesecloth, cut in half (approximately 1 yard) 1 sheet pan 1 rack to fit in sheet pan
Make space in back of refrigerator for 7 to 10 days at a steady temperature of 38 degrees F.
Remove roast from packaging and rinse well. Pat completely dry, wrap with 3 layers of cheesecloth. Place on a rack fitted inside a sheet pan in back of the refrigerator, fat side up. After 24 hours, remove, unwrap, discard cheesecloth and wrap with a fresh piece. Place back in the refrigerator for 6 to 9 days undisturbed. Make sure to check your refrigerator for temperature accuracy prior to dry aging. Keep in bottom/back of refrigerator and if possible, a refrigerator that doesn't get opened often.
Remove roast from refrigerator. Remove cheesecloth, cut away the fat and trim the ends and any discolored parts of roast.
Preheat a grill to medium-high heat.
Slice roast into 6 (1 1/2-inch thick) steaks. Season with salt and freshly cracked pepper. Cook steaks for 4 minutes on first side, turn and cook 3 minutes more. Transfer to a serving platter. Top with Horseradish Gremolata and let rest 5 minutes.
In a medium bowl, whisk butter with garlic, horseradish, vinegar, zest and salt. Stir in the parsley.