This dish is an absolute comfort food and always a crowd pleaser; it's a casserole that kids and grown-ups go crazy for.
Technique tip: Simmer or steam the chicken breasts to keep them soft and tender.
Swap option: Instead of making creamy mushroom sauce (step 3) you can use canned cream of mushroom soup.
Preheat oven to 350°F.2.
Place cooked chicken in a 9- by 13-inch casserole dish.3.
Heat a medium sauté pan over high heat. Add 2 tablespoons of the butter, when it starts to foam, add the mushrooms. Cook for 5 to 8 minutes, until the mushrooms begin to take on a golden brown color and all the moisture has cooked off. Add the onion, salt, pepper and thyme and cook 5 minutes more until the onion is soft. Add the chicken broth, bring to a boil, reduce heat to medium and reduce liquid by at least two thirds over medium heat (there should only be about 3/4 cup liquid left in the pan). Transfer the liquid to a medium saucepan. Add remaining 4 tablespoons butter and gently stir in over medium heat until melted. Whisk in the flour and the nutmeg. Stir for a minute and add the cream. Cook over low heat for 7 minutes and let cool.4.
Stir together mushroom sauce and sour cream. Pour over the chicken.5.
In a separate bowl, stir together the crushed crackers and melted butter. Sprinkle over the chicken and sauce. Sprinkle the poppy seeds on top.6.
Bake for 20-30 minutes in the preheated oven, until the top of the casserole is browned and the sauce is bubbly. Serve plain or over lemon rice.