Cooking the pasta according to the package directions.

While its cooks, whisk together the egg and milk in a bowl.

When the pasta is cooked, drain and return to the pot over medium heat. Stir in the butter until melted.

Then mix in the egg/milk mixture, stirring quickly so the egg does not scramble.

Now stir in the cheese, about an ounce at a time, so the cheese melts nice and smooth. When it has totally melted, stir in the salt, pepper, and pesto. Serves 4 as a main dish.