To keep mac and cheese creamy, add heavy cream to the recipe along with creating an easy roux. Also, avoid baking the mac and cheese to keep it from drying out and use a recipe like this one, where it is created on the stovetop. Saving a half cup of pasta water is also a great way to keep it creamy. If it sits on the stove for longer than expected, add in a few tablespoons of pasta water to get the creaminess again!