Fill sous vide tub with water and heat to 130°F. Meanwhile, season steaks with salt and pepper.
Place the steak in a bag with a sprig of rosemary. Vacuum seal the bag.
Place the bagged steak in the water. Clip it to the edge. Cook for 2 hours.
Remove the bag from the water and dry it off. Place it in the refrigerator. In the meantime, heat a skillet.
Add the steak to the pan with the butter and rosemary. Sear for 3-5 minutes on each side.
Allow to rest 5-10 minutes before slicing against the grain and serving. Enjoy!