Pat dry your fillet really well until no liquid is soaked into the kitchen towel
Rub the fillet with salt and pepper and then coat with the 1 tbsp olive oil, make sure to massage the seasoning and the oil into the meat really well
Don't cook it before you want to serve it. 30 minutes before serving, preheat your oven to 180C
Heat a griddle on the stove, or a pan, really well until smoking hot
Place the fillet onto the griddle and leave it untouched for 5-8 minutes until the fillet forms a brownish crust
Flip the fillet and do the same on the other side, this ensures the juices remain inside the meat while cooking in the oven
After searing it, place it in an oven proof pan (if your griddle is not already oven proof) and cook it for 10-12 mins if you want it rare
Cook it for 15-20 if you want it medium rare
If you have an oven thermometer place it in the middle of the cut, if it reads 75C then it's rare
Remove the meat and place on a chopping board, cover with aluminum foil and let it rest for 10 minutes so that when you cut into it the juices don't go out
10 minutes later slice into it and serve with some salt and freshly ground black pepper. Garnish with fresh rosemary if desired