MenuOption2

Course.cs

public class Course : ValueObject<Course>
{
    private string name;
    private int defaultPriority;

    public Course(string name, int defaultPriority)
    {
        this.name = name;
        this.defaultPriority = defaultPriority;
    }

    public int DefaultPriority
    {
        get { return defaultPriority; }
        private set { defaultPriority = value; }
    }

    public string Name
    {
        get { return name; }
    }
}

Menu.cs

public class Menu : Entity<Guid>
{
    private readonly IDictionary<Product, Course> products = new Dictionary<Product, Course>();

    public void AddProduct(Product product, Course course)
    {
        try
        {
            products.Add(product, course);
        }
        catch (ArgumentException e)
        {
            throw new InvalidOperationException("The product has already been added", e);
        }
    }

    public void RemoveProduct(Product product)
    {
        products.Remove(product);
    }

    public IEnumerable<Product> Products
    {
        get { return products.Keys; }
    }

    public IEnumerable<Course> Courses
    {
        get { return products.Values.Distinct(); }
    }

    public IEnumerable<Product> GetProductsForCourse(Course course)
    {
        return products.Where(pair => pair.Value == course).Select(pair => pair.Key);
    }
}

Product.cs

public class Product : Entity<Guid>
{
    private readonly string name;

    public Product(string name) : base(Guid.NewGuid())
    {
        this.name = name;
    }

    public string Name
    {
        get { return name; }            
    }
}