Season the chicken with salt and pepper on both sides. Make sure it's at room temp so it cooks properly.
Heat the oil in your pan and then when hot add the chicken and pan fry for about 3-4 min on each side. Once cooked remove from the pan and deglaze the pan with water (about 30ml or so) and then add in the mustard and mix everything well.
Finally add in the heavy cream and also the resting juices from the chicken and cook for 1-2 minutes. Taste your sauce for seasoning and season accordingly. That's it's your sauce is done. Serve the chicken and pour the sauce over.