Let’s start by preparing the chicken casserole. Place the chicken breast on a cutting board and slice it into 1-inch thick strips.
Add the chicken strips and season them with salt and pepper in a bowl. Coat well with the all-purpose flour.
Take a skillet and saute the chicken strips until lightly golden on both sides. Set them aside.
Take a casserole baking dish (13x9) and fill it with the sauteed chicken strips.
Add olive oil, thickly sliced mushrooms, and onions to the same skillet and let them saute until they are soft.
Add minced garlic to this mixture and stir for 1-2 minutes.
Transfer this mixture to the casserole baking dish and spread it over the chicken.
Moving on to the sauce preparation, take a pan, add unsalted butter, and let it melt.
Add all-purpose flour and whisk it well for at least one to two minutes.
Add the chicken stock, lemon juice, and black pepper, and let it simmer for a few minutes.
Add the milk and heavy cream and give it a good stir. Add salt to taste.
Now pour this sauce over your chicken in the baking dish.
Cover the dish with foil paper and set the oven temperature to 350 degrees. Place the dish inside the oven and let it bake for about 45 minutes.
Your creamy chicken casserole is baked. Garnish with some parsley leaves and serve hot.