Substitute fillet with sirloin, ribeye or rump steak.
Pre-heat the oven to 200°C/390°F.
To make the tarragon salt, combinethe tarragon leaves, salt flakes and freshly ground black pepper in a small bowl and set aside.
Heat a large frying pan over a high heat, add a splash of olive oil and evenly brown the fillet on all sides. Sear the ends for only a few seconds to seal in the juices. It should be rare on the inside.
Transfer the beef to an oven safe dish or baking tray and coat the whole fillet with 2/3 of the tarragon salt, reserving some for serving.
Cook in the preheated oven for approximately 15 minutes for medium rare.
Leave the fillet to rest for half its cooking time before slicing it into thick rounds.
Serve with the remaining tarragon salt and your choice of sides.