Sear the tournedos in butter for approximately 1 minute on each side. Bake in 350° oven until desired doneness (approximately 10 minutes for medium).
Cook the apples and onions in a pan with olive oil until apples are tender, approximately 5 minutes. Add the crumbled blue cheese, parsley and chives and continue cooking for 1 minute to combine flavours.
Garnish your cooked tournedos with the topping and serve with the creamy fennel salad.