1) Heat a pan very well and add olive oil. Sauté beef fillet in all sides well, adding salt. 
2) When the fillet gets a nice colour, add glove of garlic, thyme, rosemary and butter. Lower temperature and with a spoon keep pouring melted butter all over the fillet until you get a nice caramelized dark colour.
3) Take meat out of the pan and let to rest for 4-5 minutes while you make the pepper sauce.
4) In the same pan, where you cooked the meat, whip the  surface with kitchen paper and add chopped onion and mixed pepper corns.
5) Reduce with wine and Worcestershire sauce and slowly thicken it with butter.