Melt butter in a large skillet over medium heat. Add pears and sauté until lightly golden. Remove pears and set aside. Do not clean the skillet.
Season pork medallions with salt and pepper and coat them with flour. Add medallions to the same skillet over medium high heat until browned on both sides. Remove pork from skillet and transfer to bowl with pears.
Add chicken broth, port and mustards to skillet and bring to a boil. Reduce for 5 minutes until sauce thickens lightly. Return pork and pears to the skillet and cook until pork is tender. If necessary, thicken sauce with 1 tablespoon flour diluted in ¼ cup cold water.
Correct seasoning and serve.