Photo: Nielsen Massey
Place the beef in a freezer bag. Using a rolling pin, tenderise the fillet until it's 1cm thick. Do not be too rough as you will shred the meat. Remove the meat from the bag and place it on a chopping board. Rub both sides of the meat with a little salt and pepper, the cacao cruet and the vanilla bean paste. Place back in the bag and zip it up, then place it in the fridge and leave it to marinate for a few hours, or overnight.
Preheat the oven to 200°C/fan 180°C/gas mark 6. Trim and quarter each slice of brioche. Place on a baking tray and drizzle the slices with olive oil. Bake for 10 minutes or until toasted and golden in colour.
Heat the butter in a large frying pan. When piping hot and the butter has turned into a buerre noisette, place the marinated steak into the pan and cook for 5-6 minutes on each side. Leave the meat to rest on a clean chopping board for 5 minutes and then slice it. Add it to the brioche and place a few coriander leaves on top to serve.