I made one pot mac & cheese tonight and will certainly make it again. It was pretty simple as long as you're willing to stand in the kitchen and stir a lot; kind of like with risotto. You put the macaroni and milk in the pan and cook on low while the macaroni absorbs the milk. This means no making a bechamel and no need for cream and butter (though I did add a small bit of butter). The starch from the pasta along with the evaporation from the milk creates the thickness. I didn't have elbow mac and used some small penne from TJs. Perhaps that pasta is bigger but I found I needed about twice as much milk as called for. That is fine since, like risotto, you can just keep adding liquid as you go. I also put in a little more cheese - maybe 1/3 cup or so. Next time I'll probably have it be a bit more liquid when I cover and let set so it isn't too thick. When my pasta was done, I tossed in some broccoli and tuna and had myself a nice one pot meal. Delicious!
Update: Not so good as a leftover. It gets a little to mushy.