Chop onions.
Put the onions in a pan preheated with butter and cook until transparent, stirring occasionally.
Cut the chicken fillet into small cubes and add to the onions. Cook slightly over medium heat.
Cut the mushrooms into pieces, put them in the pan, mix and cook for 5 minutes, season with salt and pepper.
Pour in the cream, add the sour cream and cook until thickened. Salt to taste.
Add chopped parsley to the finished bowl.
Serve with mashed potatoes.