Cook the pasta according to package directions while you make the chicken and sauce. Drain and keep in the colander.
Meanwhile, melt the butter in a very large skillet over medium-high heat. Add the chicken in batches if necessary (you don’t want to crowd the pan), season with salt and pepper, and sauté until mostly white on the outside but not cooked through, about 2 minutes. Remove the chicken and set aside on a plate.
Do not clean the pan! Those brown bits on the bottom of the pan are going to add flavor to the sauce. Add the scallions to the pan and sauté over medium heat for just 1 minute, then add the garlic and sauté for 1 more minute. Turn the heat to high, immediately add the chicken broth, and scrape the bottom of the pan to loosen up all of those delicious, caramelized bits. Add the cream and bring to a simmer. Simmer for 6 to 10 minutes, until the sauce has reduced and thickened up a bit.
When the sauce has reduced a bit, stir in the partially cooked chicken, 1 cup Parmesan, and ¼ teaspoon red pepper flakes (or more to taste). Cook, stirring frequently, for 2 more minutes until the chicken is cooked through and everything is nicely blended. Taste and adjust the seasonings.
Return the pasta to the pot it was cooked in and pour in the sauce and chicken. Add half of the parsley and toss until the pasta is nicely coated with the sauce and everything is well blended. Transfer the mixture to a serving bowl and sprinkle with the remaining parsley. Pass extra Parmesan and red pepper flakes at the table.
Notes
While it’s certainly reasonable to thrill over a meal of reheated leftover Alfredo pasta, either warmed on the stovetop or in the microwave, this dish is best when it’s made just before serving. However, you can keep leftovers for up to 3 days and reheat them in a pot over medium-low heat, stirring frequently. You can also reheat it in the microwave until just heated through.
As soon as you put the pasta water on to boil, start sautéing the chicken, and then make the sauce. The pasta should be done when the sauce is ready.
After you sauté the chicken, do not clean the pan! Those brown bits on the bottom of the pan are going to add flavor to the sauce.
Variations When you add the Parmesan, you can add any of the following to the pot, alone or in combination, and stir over medium heat for another minute or two.
Or, you can serve up portions of Chicken Alfredo Pasta for those who like it plain and simple, then add proportionate amounts of any of the add-ins to the pot.