Season the chicken with salt and black pepper.
Heat the oil in a medium pan over medium heat and brown the chicken on all sides. Remove and set aside.
In the same pan, sauté the onion until soft and translucent. Add the garlic and cook briefly.
Add the tomato paste, ketchup, and mustard, stirring to combine.
Return the chicken to the pan and add the mushrooms, if using.
Lower the heat and pour in the cream. Stir gently and simmer for 5–7 minutes, until the sauce thickens slightly.
Taste and adjust seasoning if needed. Serve hot.
