Place carrots in a skillet; add 1 in. of water. Bring to a boil. Reduce heat; cover and simmer for 15-20 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.Place the removed carrot in a food processor; cover and process until finely chopped. Transfer to a large bowl; add mayonnaise, onion, horseradish, nutmeg, salt and pepper. Spoon into carrot shells.
Place in a greased 13-in. x 9-in. baking dish. Combine the crumbs, 1 tablespoon butter and paprika; sprinkle over carrots. Drizzle with remaining butter.
Bake, uncovered, at 375° for 20-25 minutes or until tender.