Preheat oven to 400°F (200°C). Grease a 9x13 inch baking dish.
If using chicken breasts, cut into 2-3 large pieces. Pat chicken dry.
In a food processor, pulse crackers, cheese, salt, pepper, garlic powder, and parsley into fine crumbs. Transfer to a shallow dish.
In another shallow dish, whisk eggs and 2 tbsp milk.
Dredge each chicken piece in egg wash, then press firmly into crumb mixture to coat completely. Place in baking dish.
Lightly spray chicken with cooking spray. Cover dish tightly with foil and bake for 20 minutes.
Remove foil and bake uncovered for 10 more minutes, or until chicken is cooked through (165°F) and coating is golden and crispy.
For the sauce: While chicken bakes, combine soup, sour cream, and butter in a saucepan over medium heat. Stir until hot and smooth. Thin with milk, 1 tbsp at a time, until desired consistency is reached.
Serve chicken drizzled with warm sauce.