Preheat the oven at <temperature>240<unit>°C</unit></temperature>

Mix <quantity>3<unit>tbsp</unit></quantity> of mustard, <quantity>¼<unit>cup</unit></quantity> of Worcestershire sauce, salt, and black pepper to taste in a large bowl

Coat a whole <quantity>1<unit>kg</unit></quantity> eye of round roast with the mixture. Cover and let in rest in the refrigerator for 2h to marinate

Sear all sides of the meat on a skillet over high heat, adding vegetable oil as needed. Transfer the seared meat to a roasting tray

Cover with aluminium foil and roast for 10m

Let it cool down and refrigerate until cold

Thinly slice the meat. The roast beef is ready

Melt <quantity>1<unit>tbsp</unit> of butter in a frying pan and add <quantity>2</quantity> brioche slices. Toast the bread

Add mayonnaise to taste to a slice. Spread Dijon mustard to taste on the other slice

Place <quantity>6</quantity> slices of the Roast Beef on one slice of bread

Add arugula leaves and red onion pickles to taste over the meat. Cover with the other slice of bread

Cut the sandwich in half and plate. Garnish with mayonnaise and sliced scallions to taste. The roast beef sandwich is ready

Enjoy!