1Place in crock-pot, sprinkle with salt and pepper; top with onions. Combine the ketchup, mustard and celery seeds; spread over meat. Cover and cook on low for 8-10 hours, or until tender. Remove and keep warm. Transfer cooking juices to a blender; cover and process until smooth. Serve with brisket, thinly sliced across the grain. Makes 6 servings.