Cut the chicken breast fillets into bite-sized pieces. Salt, pepper and sauté. Cut the onion into small pieces and add. Quarter the mushrooms and add them to the pan. When everything is well seared, deglaze with the stock and white wine and simmer for about 10 minutes. Mix 1-2 tablespoon mustard with créme fraiche and stir into the shredded meat. Let it simmer again briefly.