Preparation Steps

• Heat the oven to 375°F and lightly coat a 9×13-inch baking dish with cooking spray.
• Poach the chicken: Bring the chicken broth to a gentle simmer in a medium pot. Stir in poultry seasoning, 1/2 teaspoon salt, and black pepper. Slide in the chicken breasts and simmer (do not boil hard) for 12–15 minutes, or until the centers reach 165°F. Transfer chicken to a board and tent with foil to rest.
• Par-cook the potatoes: Return the broth to a boil and add the diced potatoes. Simmer 6–7 minutes until just fork-tender but not fully cooked. Drain well, reserving 1/2 cup of the broth. Spread potatoes on a towel-lined tray to steam off excess moisture.
• Mix the topping: Stir the panko with melted butter until the crumbs look evenly moistened and sandy; set aside.
• Make the creamy base: In a large bowl, whisk together the cream of chicken soup, cream of potato soup, sour cream, garlic powder, Dijon, and 1/4–1/2 cup reserved broth until smooth and spoonable. Fold in the frozen mixed vegetables and 1 1/4 cups of the cheese. Taste and add a pinch more salt if needed, keeping in mind the cheeses and soups are salty.
• Chop the rested chicken into 3/4-inch pieces. Gently fold the chicken and drained potatoes into the creamy mixture until evenly coated. Scrape into the prepared baking dish and level the top.
• Cover tightly with foil and bake for 25–30 minutes, until the edges are bubbling.
• Uncover, sprinkle on the remaining 1/2 cup cheese, then scatter the buttery panko evenly over the surface. Bake 10–12 minutes more until golden. For extra color, broil 1–2 minutes, watching closely.
• Let the casserole rest 10 minutes before serving so the sauce sets and slices cleanly.