Sous Vide Pork Tenderloin

1. Stage

Prepare a thermocirculator and water bath according to manufacturer's directions. Set thermocirculator to 135 degrees F (58 degrees C); if you want pork cooked medium instead of medium-rare, set to 145 degrees F (63 degrees C), and allow water bath to come up to temperature.

2. Stage

Combine onion, wine, butter, Dijon mustard, vinegar, lemon juice, whole grain mustard, turbinado sugar, lemon zest, salt, and 1/2 teaspoon tarragon in a medium microwave-safe bowl. Place in microwave and cook on high power until butter melts and sugar dissolves, stirring halfway through, about 1 minute. (This yields 1 1/2 cups sauce).

3. Stage

Place tenderloins in a vacuum-sealable bag with 3/4 cup of the mustard mixture and massage contents of bag to ensure meat is coated evenly in sauce, spacing tenderloins in a single layer in the bag. Seal bag with a vacuum sealer according to manufacturer's directions.

4. Stage

Transfer vacuum-sealed tenderloins to warm water bath with thermocirculator; cover vessel with aluminum foil to reduce evaporation. Cook to desired doneness, 45 to 50 minutes; meat will be 135 or 145 degrees F (58 to 63 degrees C) when done depending on desired doneness.

5. Stage

Remove bag from water bath, transfer meat to a plate and pat dry with a paper towel. Rub with olive oil and sprinkle with pepper.

6. Stage

Heat a large nonstick skillet over medium-high heat. Sear tenderloins in skillet until deeply browned on all sides, 3 to 4 minutes on each side. Transfer to a cutting board to rest for 5 minutes. Wipe skillet clean with a paper towel if any drippings are too dark.

7. Stage

Reduce heat to medium. Add remaining 3/4 cup mustard sauce to skillet and allow to come to a simmer, reducing until slightly thickened, 1 to 2 minutes. Add cream and remaining 1/2 teaspoon tarragon to skillet, and cook, stirring occasionally, until sauce has thickened enough to coat the back of a spatula, about 1 minute. Slice tenderloins and serve with sauce.