Fill a large pot or container with warm water and heat the water bath to 139° F (or the desired temperature on the chart) according to your sous vide machine's instructions.
Season the pork tenderloin very liberally with kosher salt and freshly ground black pepper and place in a vacuum seal bag or ziplock bag with a few thyme and rosemary sprigs on each side.
Vacuum seal the bag if using a vacuum sealer, or if using a ziplock bag; use the water displacement method by partially sealing it removing as much air as possible, then place it in the water to push the rest of the air out before sealing.
Clip the bag to the side of the pot or container to keep it submerged and cook for 1 1/2 hours to 4 hours.
Remove from the water bath remove the pork from the bag. Dry well with paper towels.
Heat a heavy-bottom skillet over high heat and drizzle in enough canola oil to coat the bottom. Sear for 30 seconds on each side to brown, 2 minutes total. While the pork sears, add a few tablespoons of butter and more fresh herbs and baste the butter over the pork as it browns.
Rest for a few minutes before slicing and serving immediately.