Beat chicken breast until heavy. In a bowl, mix chicken seasonings. Season the chicken breasts on both sides.
Heat 2 Tbsp of oil in a skillet over medium / high heat. Sear chicken for 2-3 minutes per side. Turn the heat to low and cook for another five min until the chicken is tender and perfectly cooked.
In the meantime, peel the potatoes in thin slices. Sauté the potato over medium/high heat for around ten min or until the potatoes are tender. To taste, season the potatoes with salt and pepper.
Remove the chicken from the skillet and cover to keep it warm. In the same pan, sauté the mushrooms with the chopped onions and the garlic. Cook till the mushrooms are golden, salt, and pepper to taste.
In a bowl, mix the sour cream, egg, mayo, milk, salt, and pepper.
When the potatoes are tender, put them in a saucepan. Spread them uniformly around the bottom of the casserole dish. Top with some sliced greens.
Cut the chicken breast into small slices. Eared over the potatoes in the casserole dish. Top chicken with a combination of mushrooms. Put 4 tablespoons of butter in the dish.
Mix all the ingredients for the sauce and pour the sauce over the casserole dish. Attach the cheese and cover with foil.
Bake at 400 ° F for 35 minutes, remove the foil and bake for another 10 minutes. Put more herbs and serve well.