Using a very sharp knife, keeping knife parallel to cutting board, slice chicken breast halves in half horizontally.
Sprinkle chicken with pepper and using 1 tablespoon of the mustard, spread 1 side of each piece of chicken.
Cook chicken in hot oil in nonstick skillet over medium heat, when chicken looks cooked around edges and the center color is beginning to look slightly cooked, flip chicken pieces over and cook other side. This should take around 5 minutes total (cut into the thickess piece of chicken to check that there is no more pink).
Remove chicken from skillet and set in barely warm oven or cover with foil and put in warm place.
Combine whipping cream and remaning mustard, wine, and peppercorns in skillet. Bring to a boil, and cook until mixture thickens. Spoon sauce over chicken. Yield 4 servings (2 pieces of chicken each)