Fill a large pot with water. Attach a sous vide stick to the pot and set the heat to 129°F, for medium rare (for other temperatures, see the temperature chart in the notes below).
Place a tri tip steak in a ziplock bag or vacuum seal bag.
Season the steak with steak seasoning, then add pats of butter, fresh rosemary sprigs and crushed garlic cloves to the bag.
Use a vacuum sealer to seal the bag shut or use the water displacement method to seal the bag.
To use the water displacement method, simply place the bag with the steak in it almost all of the way under the water, leaving just about an inch of the top of the bag open. The water will press out all of the air around the food in the bag, you can then seal the bag closed.
Once the steak is sealed in the bag with the herbs and seasonings, place it in the sous vide water bath for 6 hours.
After 6 hours, remove the tri tip steak from the bag and discard the fresh rosemary sprigs.
Heat a grill or grill pan on the stove over high heat.
Sear the tri tip on each side for 30-60 seconds.
Season lightly with salt and pepper while the steak is searing.
Remove the tri tip from the heat, cover with foil and let rest for 10 minutes before slicing.
When slicing the tri tip, you’ll notice that the grains run in different directions on the tri tip. Slice the long triangular tip from the other end of the tri tip where the grains intersect, then slice each piece of the tri tip against the grain.