01 - Preheat your oven to 375°F (190°C). Lightly grease a 9x13-inch baking dish.
02 - Boil pasta in generously salted water until it reaches an al dente texture. Drain thoroughly and set aside.
03 - In a medium saucepan, melt 2 tablespoons of unsalted butter over medium heat. Whisk in the all-purpose flour and cook for 1 minute, stirring constantly to form a paste. Gradually incorporate the whole milk, whisking continuously until the mixture thickens slightly, approximately 3–4 minutes.
04 - Reduce the heat to low. Stir in the shredded cheddar cheese, sour cream, Dijon mustard, garlic powder, onion powder, black pepper, and salt. Continue to cook, stirring, until the cheese is fully melted and the sauce is smooth and creamy.
05 - In a large mixing bowl, combine the cooked pasta, shredded chicken, chopped dill pickles, and the prepared cheese sauce. Stir gently until all components are evenly coated. Transfer this mixture into the prepared baking dish, spreading it out uniformly.
06 - In a small bowl, combine the crushed pickle chips, panko breadcrumbs, 2 tablespoons of melted butter, and fresh dill (if using). Mix well to ensure the breadcrumbs are moistened. Sprinkle this mixture evenly over the surface of the pasta and chicken.
07 - Place the baking dish in the preheated oven and bake, uncovered, for 25–30 minutes. The casserole is ready when the topping is golden brown and the filling is visibly bubbling.
08 - Remove the casserole from the oven and allow it to rest for 5 minutes before serving. Garnish with chopped fresh parsley just before serving, if desired.