public class RecipeBook
{
    public List<Recipe> Recipes { get; set; }

    public RecipeBook()
    {
        Recipes = new List<Recipe>();
    }
}

public class Recipe
{
    public DateTime LastModified { get; set; }
    public DateTime Created { get; set; }
    public string Instructions { get; set; }
}

public void SomeFunction()
{
    RecipeBook recipeBook = new RecipeBook();

    var myRecipe = new Recipe()
    {
        Created = DateTime.Now,
        LastModified = DateTime.Now,
        Instructions = "This is how you make a cake."
    };

    recipeBook.Recipes.Add(myRecipe);

    var doc = new XDocument();
    using (var writer = doc.CreateWriter())
    {
        var serializer = new XmlSerializer(typeof(RecipeBook));

        serializer.Serialize(writer, recipeBook);
    }

    doc.Save(recipesFileFullPath);
}