Bring a large pot of salted water to a boil over high heat. Add elbow macaroni and cook until al dente, about 7-8 minutes. Drain the pasta and set aside.

In a large skillet, melt 2 tablespoons of butter over medium-high heat. Add diced chicken breasts seasoned with salt and pepper, and cook for 5-7 minutes until golden brown and cooked through. Transfer to a plate and set aside.

In the same skillet, add 3 tablespoons of butter and melt over medium heat. Whisk in 3 tablespoons of flour until smooth, cooking for 1-2 minutes. Gradually pour in 2 cups of milk, whisking continuously until thickened, about 4-5 minutes.

Remove from heat and stir in 2 cups of shredded cheddar cheese until fully melted and smooth. Adjust seasoning with salt and pepper if needed.

Fold the cooked macaroni and sautéed chicken into the cheese sauce until well coated.

For an extra crispy top, transfer to an oven-safe dish, sprinkle breadcrumbs on top and bake in a preheated oven at 350°F (175°C) for 20 minutes.

Remove from the oven, let cool for a few minutes, and garnish with chopped fresh parsley. Serve warm.