Warm Beef Salad

1 X 700g piece beef fillet 1 red onion, peeled and cut lengthways into eighths 1 punnet large cherry tomatoes, quartered Tarragon vinegar 2 cups baby spinach leaves ½ cup black olives Salted baby capers, rinsed, to taste   Preheat the oven to 220C.  Rub the beef with olive oil and season well with salt and pepper.  Place the beef and onion in an oiled baking dish and roast for 7 minutes, then reduce heat to 180C and cook for 20 minutes or until beef is medium rare. Meanwhile, place the tomatoes on an oiled baking tray and roast for 20 minutes.  Remove the beef and tomatoes from the oven.  Set aside the beef in a covered dish.  Deglaze the baking tray with a little tarragon vinegar and set aside.  When the beef is cool enough to handle, carve into thin slices.  Place the spinach, olives, tomatoes, onion and capers in a bowl and dress with the beef juices.  Combine, then toss through the beef and serve immediately.