I hadn't made macaroni and cheese in years and this looked very easy. I don't know the reason, but it was not a creamy texture, but more like crumbly or curdled. Could someone please tell me what I might have done wrong. The sauce was creamy when I mixed it. Also I used mild cheddar as I did not want the cheese to over power. I used the cheese on top and a few buttered bread crumbs, which I liked. Help cause I would like to know the reason for the curdling.