Combine steak tips, balsamic vinegar, olive oil and rosemary in a large ziploc bag. Season to taste with salt and pepper. Marinate steak tips in the fridge for 2-24 hours.
Remove steak from marinade. Discard marinade. Heat 2 tbsp of oil in a cast iron on medium-high heat. Add steak tips and cook until browned on all sides.
Place cast iron skillet under the broiler for a few minutes to get a crispy charred exterior if desired. Serve and enjoy!