30 minutes before cooking, remove the beef from the refrigerator. Pat dry with paper towels and season generously on all sides with salt, pepper, and the spice blend. Preheat the oven to 400°F. Line a sheet pan with foil. Transfer the seasoned beef to the sheet pan. Roast 28 to 30 minutes, or until an instant-read thermometer registers 110°F.* Remove from the oven.  

*This cook time will yield a final internal temperature of 125°F (medium-rare) after Step 2. The USDA recommends a minimum safe cooking temperature of 145°F for beef. Roast the beef an additional 4 to 6 minutes to achieve this.Consuming raw or undercooked meat, poultry, fish, seafood or eggs may increase your risk of foodborne illness.

In a large pan (nonstick, if you have one), heat a drizzle of olive oil on medium-high until hot. Add the roasted beef. Cook 2 to 3 minutes per side for medium-rare (125°F), or until browned and cooked to your desired degree of doneness. Leaving any browned bits (or fond) in the pan, transfer to a cutting board and let rest at least 15 minutes.

While the beef rests, wash, dry, and thinly slice the chives. Heat the pan of reserved fond on medium-high until hot. Add the broth (carefully, as the liquid may splatter), mustard, worcestershire sauce, vinegar, crème fraîche, and beef concentrate. Cook, whisking occasionally, 5 to 6 minutes, or until slightly reduced in volume. Turn off the heat. Whisk in the butter until melted and combined. Stir in half the sliced chives. Find the lines of muscle (or grain) on the rested beef; slice crosswise against the grain into 1/2-inch-thick slices. Serve the sliced beef with the pan sauce. Garnish the sauce with the remaining sliced chives.