Add broth, sun-dried tomatoes, and butter to a medium saucepan and bring to a boil over medium-high heat. Stir in contents of stuffing mix pouch. Cover saucepan and remove from heat. Let stand 5 minutes. Fluff stuffing with fork. Let stuffing cool completely. Preheat oven to 425 degrees F. Lay steak flat on clean work surface and sprinkle with salt and pepper. Cover steak evenly with stuffing. Roll up steak lengthwise to create a pinwheel effect, enclosing stuffing completely. Skewer seam with toothpicks. Place the steak roll, seam side down, on a foil-covered cookie sheet. Sprinkle roll with salt and pepper. Roast until steak is golden brown and cooked through, about 40 minutes.
Rosemary Mashed Potatoes:
While steak is cooking, transfer potatoes from package into a medium saucepan. Add butter, milk, and rosemary, and warm over medium-low until completely heated through. Season, to taste, with salt and pepper.