In a medium bowl, combine the Maine crabmeat, ½ cup breadcrumbs, egg, mayonnaise and chopped relish. Stir in the horseradish and celery salt. Season to taste with fresh pepper. Using a scoop or measuring cup, divide the batter into 6 portions. It will be fragile, but should stick together. In a shallow pan, add the remaining ½ cup breadcrumbs. Dredge each crab portion in the crumbs on both sides, flatten them slightly. Heat an ovenproof pan on top of the stove. Brown the crab cakes on each side, and then place the pan in the preheated 450-degree oven. Bake until set and crispy, about 15 minutes.