Cut your onions and mushrooms and set aside.
Cut your chicken into strips and set aside.
Fry your chicken pieces in a deep frying pan on medium high heat. Then set aside.
Saute your onions in butter until they are opaque.
Add your mushrooms to the pan and saute until they are soft and release juice.
Sprinkle flour over the mushroom mixture and stir, making sure there are no lumps. Cook for 1 minute.
Add tomato paste to the mushroom mixture and mix well.
Add your fried chicken strips to the mushroom mixture and stir well.
Add ground mustard, paprika and brandy. Stir and allow the alcohol to slightly cook out for about 1 minute.
Add chicken stock/broth and stir.
Add salt and pepper to taste.
Stir in your sour cream and serve over potatoes, egg noodles, rice or pasta.