Fill a large pot with salted water and bring it to a rolling boil over high heat. Add the elbow macaroni and cook according to package instructions, usually around 8-10 minutes, until al dente. Drain the pasta in a colander and set it aside.

Heat a large skillet over medium heat, adding the butter to melt. Once melted, season the chicken breasts with salt and pepper, and place them in the skillet. Cook for 5-7 minutes on each side, until golden brown and cooked through, reaching an internal temperature of 165°F (74°C). Remove the chicken and let it rest before slicing into bite-sized pieces.

In the same skillet, add an additional tablespoon of butter over medium heat. Once melted, whisk in the flour to create a roux, cooking for about 1 minute until bubbly and lightly golden. Gradually pour in the milk while whisking continuously, allowing the mixture to come to a simmer and thicken for about 4-5 minutes, creating a velvety base for your creamy chicken mac and cheese.

Once the cheese sauce has thickened, lower the heat and gradually stir in the shredded cheddar cheese, mixing thoroughly until it's completely melted and smooth. Take your time to ensure there are no lumps for a luscious, creamy texture.

Fold the cooked elbow macaroni and the sliced sautéed chicken into the cheese sauce, ensuring every piece is well-coated. Stir gently for 1-2 minutes until evenly combined and heated through.

For an added crunchy topping, preheat your oven to 350°F (175°C). Transfer the mixture into an oven-safe dish, and sprinkle breadcrumbs over the top if desired. Bake for 20 minutes or until the top is golden and bubbly.

Remove from the oven and let it cool slightly. Serve warm, garnished with parsley.