In small bowl, mix up the spice rub - salt, black pepper, garlic powder, and smoked paprika. Pat the pork dry using a paper towel then rub the spices into the meat.

Heat the olive oil in large skillet over medium-high heat and sear the pork until it is browned on all sides, about 3-5 minutes per side.

Transfer the seared pork loin to a large Foodsaver bag or a large zip-top plastic bag. Remove all air from bag using a vacuum sealer or the water displacement method.

Fill a large stockpot or sous vide container 3/4 full of water. Place on heat-proof surface and add immersion circulation (sous vide cooker.)

Heat water to temperature based on your preferred doneness for your pork. (131 degrees F = rare, 136 degrees F = medium-rare, 144 degrees F = medium, 149 degrees F = medium-well, 158 degrees F = well done). I like 144 degrees for pork.

When the water is heated, lower each plastic bag into the water making sure the meat is fully submerged. Fold top of bag over the side of the stockpot. Clip bag to the side, if needed.

Set timer for cook time. Cook time depends on thickness of your pork. (2-inches = 1 hour 30 minutes, 3-inches = 3 hours, 4-inches = 5 hours).

After cook time is finished, remove bags from sous vide and remove pork from bag. Preheat heavy skillet over high heat. Place 1 Tbsp butter or olive oil in skillet then sear pork 1 minute on each side.

Let pork roast rest 10 minutes before slicing and serving.