Cheesey Scalloped Carrots

8 C of sliced carrots
1/4 C of butter or margarine
1/2 C of chopped onion
1/4 C of flour
1/2 tsp celery salt
1/4 tsp paprika
2 tsp prepared mustard
2 C of milk
2 C of grated low fat sharp cheddar cheese
salt and pepper to taste
1/2 C of crushed garlic croutons or equal amount of breadcrumbs
2 T melted margarine

Cook carrots in salted boiling water until tender. Drain. Melt a 1/4 cup of butter in a separate saucepan. Add onion and cook until clear and soft. Mix in the flour, salt, pepper, and celery salt. Stir in mustard and milk until it boils and thickens. In a 9 x 13-inch pan, layer half of the carrots, half of the grated cheese, and another layer of carrots and grated cheese. Pour over all the sauce. Top with breadcrumbs and melted butter, adding garlic to taste, or use crushed croutons. Bake uncovered at 350 degrees for 25 to 30 minutes until browned and heated through.