Remove the meat from the fridge approx. 30 mins. prior to cooking. Place the casserole dish in the centre of the oven, preheat to 80°C. Heat the butter in a frying pan. Season the meat and brown for approx. 3 mins. on each side, only turning when a crust has formed, remove from the pan. Insert the meat thermometer into the thickest part of the meat. Place the meat in the casserole dish, cook for approx. 45 mins. The core temperature should be approx. 55 °C (à point). Remove from the oven, leave to rest for approx. 10 mins., carve the meat diagonally across the grain into thin slices (approx. 3 mm).
Combine the parsley with all the other ingredients up to and including the fleur de sel.
To top the crostini
Spread the crème fraîche onto the slices of baguette, top with the roast beef and gremolata, garnish with garden cress.