No grating - just get your Colby cheese sliced to whatever thickness you want at your grocer's deli. Layer it with any macaroni (elbow works great) and then bake it until it's done (really whatever temp you desire) you can bake at 325 or 350 but just watch the first time you do it so it doesn't burn. It's simple and those are the only two ingredients. No milk at all. We like ours browned on top to get a little crunch to just the top layer.
Oh and Gruyere is great too! I just don't use any of the orange cheeses. Now that we are watching our diets and fat intake I've been using the Jarlsberg Light which is awesome. You can get that either sliced at the deli or buy in package but then you would have to slice thin at home or grate it.