Bring a large pot of salted water to a rolling boil over high heat. Add the elbow macaroni and cook for 7-8 minutes until al dente. Drain in a colander and set aside without rinsing.

While the pasta cooks, heat a large skillet over medium heat and melt 2 tablespoons of butter. Add the cubed chicken seasoned generously with salt and pepper. Cook for 5-7 minutes, stirring occasionally, until the chicken is golden on the edges and no longer pink in the center. Transfer to a plate.

In the same skillet, melt the remaining 2 tablespoons of butter over medium heat. Whisk in the flour and cook for 1-2 minutes, stirring constantly, until it becomes a light golden paste.

Slowly pour in the milk while whisking constantly to prevent lumps, and continue stirring for 4-5 minutes until the sauce thickens enough to coat the back of a spoon.

Reduce heat to low and gradually stir in the shredded cheddar cheese, one handful at a time, stirring until completely melted before adding more. Add the garlic powder and season with additional salt and pepper to taste. The sauce should be smooth and glossy.

Gently fold the cooked macaroni and chicken into the cheese sauce until everything is evenly coated. If the sauce seems too thick, add a splash of milk to reach your desired consistency.

For a baked version with a crispy top, transfer the mixture to a greased 9x13-inch baking dish, sprinkle with breadcrumbs, and bake at 350°F for 20 minutes until golden and bubbling. Let it rest for 5 minutes before serving. Garnish with fresh parsley if desired.