Season the chicken with salt and pepper. Coat in flour and shake off the excess. Reserve 1 Tbsp. of the flour.
Place the oil in a skillet set over medium to medium-high heat. Add the chicken and cook 4 minutes per side, or until just cooked through. Set the chicken on a plate. Remove any oil from the skillet. Add the wine, garlic and sage to the skillet, bring to a simmer, and reduce the wine by half. Whisk the reserved flour into the chicken stock. Add the stock mixture and cream to the skillet and reduce and simmer until a lightly thickened sauce forms. Whisk in the mustard, and then return the chicken to the skillet. Heat the chicken through a few minutes, turning once or twice. Sprinkle servings of the chicken with chopped parsley.