Creamy Chicken and Mushroom Sauce

Name: Creamy Chicken and Mushroom Sauce
Total time: 30 min
Yield: 4
Ingredients: 1 onion; salt, as needed; leek, as needed; plain flour, as needed; 2 chicken breasts; ground pepper, as needed; poultry stock, as needed; whipping cream, as needed; mushrooms, as needed; oil, as needed