Scrape carrots, cut crosswise in half,
then into thin strips, julienne style, about 1/4" wide. Add 1 tsp. salt; cook, covered, 6-8 min., or until tender.
Preheat oven to 375F. Drain carrots, reserving 1/4 c. liquid.
Turn into 10x6" (1 1/2 qt) baking dish.
In small bowl, combine onion, horseradish, mayonnaise,
1 tsp. salt, pepper, and reserved liquid.
Pour over carrots, spreading evenly.
Toss bread crumbs with butter; sprinkle over top.
Bake 15 min. Serves 6.