Start with your boneless ribeye steak. Pat it dry with paper towels to remove excess moisture.
Rub the steak all over with 2 teaspoons of salt, then sprinkle 1 teaspoon of garlic salt and minced pepper over the steak.
Place the seasoned steak into a resealable freezer bag or use a vacuum sealer. Use the water displacement method if using a bag.
Set your sous vide circulator to 129°F (54°C) for medium-rare. Submerge the sealed steak in the water bath and cook for 2 to 3 hours.
Once cooked, remove the steak from the bag and pat it dry again. Preheat your cast iron skillet over high heat.
Spread 1 teaspoon of mayonnaise on one side of the steak.
Place the mayo-coated side onto the hot skillet and sear for about 1-2 minutes. Flip and repeat on the other side.
Once seared, remove the steak from the skillet and let it rest for about 5 minutes before slicing against the grain.