Bring a medium pot of water to boil and season with salt. Boil the Brussels sprouts for two minutes, just to begin cooking and turn bright green. Drain and set aside.
Meanwhile, season the beef with salt and pepper and splash with a little of the Worchestershire sauce and sprinkle with chopped rosemary. Sear in a hot large skillet with one tablespoon olive oil for about one minute a side on medium high heat, until just browned.
Transfer to a large baking sheet, leaving half of pan empty to add sprouts . Add the sprouts beside beef and toss in the rest of the olive oil and finish cooking in a 400 degrees Fahrenheit oven for six to eight minutes until medium rare inside and sprouts are golden and tender. If beef is cooked before sprouts are done, just remove to a platter and tent until sprouts are cooked.
Meanwhile, in same skillet that meat was seared, add maple syrup , soy sauce and butter . Melt over medium high heat and add walnut halves. Season with cracked black pepper to taste and stir until liquid evaporates and walnuts are coated about two to three minutes. Remove from heat and toss with Brussels sprouts immediatley.