Dissolve 1/4 cup salt in 1 cup cold water in a medium bowl. Add the pork medallions, cover and refrigerate 1 to 4 hours.
Meanwhile, spread the fruitcake on a plate and microwave until slightly dry, 1 to 2 minutes. Chop any large pieces of fruit or nuts, then let cool. Mix the butter, mustard, Worcestershire sauce, 1/2 teaspoon salt, and pepper to taste in a medium bowl. Mix in the dried fruitcake and refrigerate until firm, about 30 minutes.
Drain the pork and pat dry. Insert a paring knife into the curved side of each medallion to create a small pocket in the middle. Open the pocket with the knife or your fingertip and tuck spoonfuls of the fruitcake stuffing inside. Secure each opening with a toothpick.
Preheat the oven to 350 degrees. Season the pork with pepper. Heat the vegetable oil in a large skillet over high heat, then add the pork and cook until golden brown, about 3 minutes per side. Transfer to a baking dish and bake until cooked through, about 12 minutes.
Wipe out the skillet. Add the sherry, then return to medium heat, bring to a boil and reduce by about half. Add the cream and simmer until thickened, about 5 minutes. Season with salt and pepper. Remove the toothpicks and slice the pork medallions in half crosswise. Serve with spinach, if desired, and drizzle with the cream sauce.
Photograph by Yunhee Kim
Recipe courtesy Food Network Magazine