Tuscan, or black, kale—known as cavolo nero in Italian—has elongated deep green crinkly leaves. If you can't find it at specialty produce markets, ordinary curly kale is a fine substitute. This marinade is also delicious with pork tenderloin or pork chops. The beef tenderloin is marinated overnight, so plan accordingly. Plus: More Beef Recipes and Tips
How to Make It
In a large glass or ceramic baking dish, combine 3 tablespoons of olive oil with the thyme sprigs and season with salt and pepper. Add the tenderloin and turn to coat. Cover the beef tenderloin with plastic wrap and refrigerate overnight. Let stand at room temperature for 1 hour before grilling. Scrape off the thyme sprigs.
Light a grill. Lightly oil the grate. Season the beef tenderloin with salt and grill it over a medium-hot fire, turning occasionally, until it is browned all over and an instant-read thermometer inserted in the thickest part of the tenderloin registers 125° for medium-rare meat, 20 to 25 minutes. Transfer the tenderloin to a cutting board and let rest for 10 minutes.
Meanwhile, in a large, deep skillet, heat the remaining 2 tablespoons of olive oil until shimmering. Add the sliced garlic and cook over moderate heat, stirring, until golden, about 2 minutes. Add the Tuscan kale and water and cook over moderately high heat, stirring, until the kale is tender, about 10 minutes. Season with salt and pepper and transfer to a bowl.
Carve the tenderloin into 1/3-inch-thick slices and arrange on plates. Serve with the kale and the Shallot Confit.