There are a few different ways that eggs can be used in mac and cheese. One way is to add an egg to the cheese sauce. This will help to thicken the sauce and make it richer and creamier. Another way is to add an egg to the pasta before it is mixed with the cheese sauce. This will help to bind the pasta and cheese together. Finally, you can add an egg to the breadcrumb topping. This will help to create a crunchy and flavorful crust.