Set the sous vide water bath to 128°F. Pat the steaks dry with paper towels then season liberally with Kosher salt and black pepper. Vacuum-seal the steaks with a small sprig of rosemary on each side of the steak; alternatively, place the steaks in a resealable plastic bag, submerge in water up to the seal line to push the air out of it, then seal.
Place the steaks in the water bath (they should sink to the bottom if you have a good seal) and cook for about 2 hours – there’s a bit of wiggle room here, so if you decide to watch a 2:15 movie during your downtime, it’ll turn out just fine.
Remove the steaks from their bags and pat dry. Open some windows, then heat a cast-iron skillet over high heat until nearly smoking; add 1 tbsp ghee, coat the skillet, then add the steaks. Sear until a crust forms, then flip and re-sear. For thick steaks, sear the sides as well. Don’t overcrowd the skillet, and work in batches if needed. Set the steaks aside.
Reduce the skillet heat to medium-high, then add the wine to the skillet. Reduce by half, stirring occasionally. While the sauce simmers, slice the steaks and scatter with some extra salt and black pepper. Once the sauce is reduced, remove from heat and stir in the cold butter; taste and add salt if needed. Plate the steaks, then pour the reduced sauce over them and serve.