Season the roast beef with salt and pepper. Heat the clarified butter in a pan and fry the meat vigorously on both sides. Then place on an oven rack and cook for 5 hours at a constant 80 ° C (convection not recommended).
A drip pan prevents the meat juices from dirtying the oven. The core temperature should have reached 65 degrees.
Mix the crumbs in a bowl with the butter, oil, mustard, salt and pepper. Pluck the herbs, chop and mix in.
Take the meat out of the oven and turn on the grill. Spread the crumbs on the meat and grill on the 2nd rail from the bottom for 4-5 minutes until golden brown.
Let the meat rest briefly and cut into thin slices.