Mix the garlic powder and onion powder in your spice shaker. If you don't have one you can skip this step.
Season the steak liberally with the garlic and onion powder on both sides.
Season liberally with the sea salt and black pepper. Make sure that you are using a coarser ground salt as table salt will not work well in this application. Season on both sides of the steak.
Press the seaonings into the steak.
Set up your sous vide cooker according to the manufacter's directions. Fill your container with water while keeping the amount of water that will be displaced when you add the bag with the steak.
Set the sous vide cooker to 130 degrees for medium rare.
Place your steak in the gallon freezer bag but do not seal it.
Lower the bag with the steak into the water and let the air be pushed out as you lower it. It helps to use tongs to push it down as the water is hot.
Once the steak is fully submerged seal the bag.
Clip the bag to the edge of the vessel so that it does not fall in and become harder to remove.
Cook for 2 hours in the water bath.
After 2 hours remove the bag with steak.
Remove the steak from the bag and pat it dry. This is a very important step as you will not be able to get a good sear if the steak is wet.
Place a cast iron or stainless steel pan over high heat. Coat the pan with vegetable oil (it has a higher smoke point). Do this with vents on as it will smoke.
When the pan is really hot add the steak and flip it often, every 30 seconds or so.
About 1-2 minutes in add in the 2tbsp of butter and baste the steak with it as you sear.
Do not exceed 3-4 minutes or you will overcook the steak. Remove when you have a nice color on the steak.
There is no need to rest sous vide cooked steak. You can cut and serve it immediately. The steak may look a little grey when first cut. It will fluoresce and turn more red as it is exposed to oxegen.