Sous Vide Steak with Mushrooms and Tarragon Butter

In a small bowl, combine the butter, tarragon and a pinch of salt. Use a fork to mash together until thoroughly combined. Set aside.

Prepare an immersion circulator for use according to the manufacturer’s instructions.

Preheat the water to 129°F (54°C) for medium-rare or 134°F (57°C) for medium.

Season the steaks generously on both sides with salt and pepper. Smash the garlic cloves with the side of a knife to flatten. Place each steak in a vacuum bag and add 1 of the garlic cloves and 1 Tbs. of the tarragon butter to each bag. Vacuum seal the bags.

When the water reaches the desired temperature, lower the bags into the water bath and clip the top of each bag to the side of the water basin. Cook for the steaks for 1 hour. (The steaks can be left in the water bath, at the cooking temperature, for up to another 3 hours before serving.)
 
Remove the bags from the water bath, transfer the steaks to a plate and discard the garlic. Pat the steaks dry and season with salt and pepper.

If using shiitake mushrooms, remove and discard the stems. Cut all the mushrooms into bite-size pieces.

In a cast-iron fry pan over medium-high heat, warm the olive oil until very hot. Add the steaks to the pan and sear, turning once, until well browned on both sides, 2 to 3 minutes per side. Transfer the steaks to a cutting board to rest.

Add the mushrooms to the same pan and sauté, stirring occasionally, until nicely browned and tender, 6 to 8 minutes. Season with salt and pepper.

Cut the steaks into slices and divide among 4 serving plates. Top each serving with an equal amount of the tarragon butter and serve immediately. Serves 4.

Williams Sonoma Test Kitchen

Make It Whole30^®: Skip making the tarragon butter. Instead of using the tarragon butter, put 1 Tbs. olive oil or ghee, 1 sprig of fresh tarragon and a smashed garlic clove in each sous vide bag before sealing. While the steaks are cooking make a tarragon pesto: In a small food processor, combine 1/2 cup (2 oz./60 g) toasted pepitas, 3/4 cup (1 oz./30 g) loosely packed fresh tarragon leaves and 2 garlic cloves; process until finely chopped. With the food processor running, slowly drizzle in 1/2 cup (4 fl. oz./125 ml) extra-virgin olive oil. Season with salt and lemon juice to taste. Serve the steaks with some of the tarragon pesto on top. Also, if desired, sauté 1/2 lb. (250 g) broccolini along with the mushrooms until tender.