In heavy sauce pan heat beef broth, chicken broth, celery, onion and green pepper. Cook gently until vegetables are just tender, about 5 minutes. In small dish, dissolve cornstarch in water. Blend into soup. Cook an additional 5 minutes. Add the ham, cheese and sauerkraut. Turn to simmer. Meanwhile, in separate pan heat the butter and half and half until warm. Add this to the soup. Season with salt and pepper. Ladle into oven-proof bowls topping with a rye crisp topped with a spoonful of Gruyere cheese. Place under broiler until the cheese is melted and golden brown. Serve hot.