In a large container filled with water, preheat sous vide precision cooker to desired final temperature, refer to chart above (130ºF for medium-rare). Allow water bath to come to temperature.

Season steaks generously with salt then add to bag with bay leaves, thyme, and garlic. Seal bag, either by using a vacuum sealer or, if using a resealable zipper-lock bag, with water displacement method. To do this, slowly lower bagged steak into a pot of water, letting pressure of water push air up and out through top of bag. Once most of air is out of bag, seal bag just above water line. Seal.

Place bag in water bath so steaks are completely submerged. If sealed correctly, steaks should sink. Secure bags to side of container with clips, making sure bag does not block intake or output sections of precision cooker.

Cook steak to desired doneness according to chart above (1–4 hours for medium rare).

Meanwhile, for the sauce, melt 2 tablespoons butter in a small saucepan over medium. Add 1 minced shallot, season with salt, and cook until softened and starting to browned, about 5 minutes.

Add ⅓ cup marsala and cook until mostly reduced and “jammy,” 4 minutes.

Stir in ¾ cup beef stock and bring to a simmer; cook until mostly reduced, 6–8 minutes. Stir in 1 tablespoon cracked pepper.

Remove from heat and whisk in ½ cup cream, return to low heat and simmer (don’t let it boil) until slightly thickened about 4 minutes. Season with salt to taste.

Preheat cast iron skillet over high heat for 5 minutes.

Remove steaks and aromatics from bags and pat dry (discard bags). Add 2 tablespoons butter to skillet and swirl to melt. Add steaks and reserved aromatics, if using, and cook just until seared on each side, about 1 minute per side for medium-rare (removing and discarding aromatics as they start to burn). Shoot for internal temperature of 135ºF.

Transfer steaks to a cutting board, slice and serve with sauce. Finish with fresh parsley, if using.