Light the grill. Preheat the oven to 450 degrees.
To prepare potatoes: Quarter potatoes lengthwise into wedges. Put them in pot and cover with cold water. Place on high flame and bring to boil. When boiling, remove from heat and strain. Run cold water over to stop cooking. Strain again. Reserve.
To prepare radishes: Place halved radishes in skillet just large enough to hold them in single layer. Add water, butter, sugar, salt and pepper. Bring to boil, turn down to simmer and cook until just tender. Transfer radishes to a bowl. Reduce liquid down to glaze. Add radishes back in, stir and reserve.
To prepare steak topping: Place breadcrumbs, Parmesan, butter, horseradish, lemon juice and pinch of salt in food processor. Blend until smooth, 3-4 minutes. Reserve.
To prepare parsley: Bring 6 quarts water to boil. Add 1/4 cup salt when boiling. Place parsley leaves in boiling salted water. Count one minute after reboil and immediately remove leaves and place in ice water bath for 3 minutes. Strain, dry and coarsely chop.
Place chopped parsley and 1/2 cup of the ice water in blender. Blend on high speed, adding extra water as necessary, until completely emulsified into thick bright green liquid, 3-4 minutes. If lumpy, pass through fine mesh strainer. Reserve.
To cook steaks and finish potatoes, radishes and parsley jus: Toss reserved parboiled potatoes with olive oil and salt and white pepper to taste. Place in roasting pan in pre-heated oven. Roast until golden brown and tender, 15-20 minutes. Meanwhile, lightly rub steaks with oil and season liberally with salt and pepper. Place on grill and cook to the desired degree of doneness. When meat is done, remove and rest for 5-10 minutes. Meanwhile, heat broiler (or turn on oven broiler as soon as potatoes are done, and reserve potatoes in a warm place.)
Liberally spread a 1/4-inch layer of horseradish topping fully atop each steak. Place in broiler until nicely browned. Meanwhile, heat briefly 1/2 cup of the parsley puree with the olive oil and roasted garlic. Whisk well and season to taste with salt and pepper. Toss warm golden potatoes with chopped chives and butter. Season to taste. Warm through radishes and toss in chopped parsley. Place roasted potatoes, a small pile of glazed radishes, and a pool of the parsley jus on each plate. Place crusted steak atop a pool of parsley and serve immediately.