Tonight we had a version of Eat Air's Old Standby. It only took about 20 minutes to prepare, and the boy and I scarfed it up. While it doesn't taste like mac and cheese, it's absolutely delicious in its own right.
My changes: I used a box of Annie's Shells and Cheese for the pasta, I left out most of the teaspoon of salt (since my bouillon was pretty salty), and I added a little lemon juice and Tobasco to the finished sauce.