Mac and Cheese with Leeks

"I got this recipe from a friend, when I mentioned that we were participating in a Mac and Cheese Cook-off over Labor Day weekend… I had wanted to make a batch ahead of time, but didn’t have a chance, so I went into it with my fingers crossed, and am pretty happy with the results! I made it right up to the point it would go in the oven… I then let it sit for almost 5 hours before baking it, and I served it to the judges straight out of the oven. It. Was. Delicious."