Pat tenderloin dry with paper towels. Trim off all silverskin — the thin, shiny membrane along one side — or the meat will curl during cooking. Season generously with kosher salt and black pepper on all sides. Add aromatics (thyme, rosemary, garlic, shallots) if desired. Bag the tenderloin with aromatics distributed evenly. Vacuum seal, or use the water displacement method with a zipper-lock bag to remove all air. No air pockets — full contact with the water bath is essential for even cooking.

Transfer to a cutting board and rest at least 5 minutes before slicing. Sous vide equalizes temp throughout, so resting is brief but still needed. Slice into ½-inch medallions and serve immediately. Safety: cook at 140°F minimum and confirm with an instant-read thermometer before searing — the sear will bring it to or past the USDA minimum of 145°F. For vulnerable groups (elderly, pregnant, young children), cook to 145°F in the bath. Avoid: skipping the pat-dry (you'll steam, not sear), cooking below 130°F, and leaving in the bath beyond 4 hours (texture turns mushy). Don't skip the sear — it delivers color and flavor sous vide can't.