Place carrots in a skillet; add 1 inch of water. Bring to a boil. Reduce heat; cover and simmer for 10-15 minutes or until crisp-tender. Drain. Cut a thin lengthwise slice out of each carrot. Scoop out carrot, leaving a 1/4-in. shell; set shells aside.
Process the removed carrot in a food processor or blender until finely chopped. Transfer to a bowl; add mayonnaise, onion, horseradish, nutmeg, salt and pepper. Spoon into carrot shells.
Place in a greased 13-in.X 9-in. X 2-in. baking dish. Combine crumbs, 1 tablespoon butter and paprika; sprinkle over carrots. Drizzle with remaining butter. Bake, uncovered, at 375 degrees for 20-25 miutes or until tender.