Photo: Davinic (CC BY-SA 4.0) via Wikimedia Commons · source
Thin roast beef (or lamb) on a crusty roll, the cut side dipped in hot pan juices, with sharp mustard. Philippe's is the original; beef on weck in Buffalo is its cousin with a salted caraway roll and horseradish.
Roast (1 hr 15 min): Heat the oven to 200 C (400 F). Rub the meat with salt, pepper and garlic powder, brown it in the oil in a roasting pan on the stove, 6 minutes, then roast to 54 C (130 F) inside, 45 to 60 minutes. Rest it on a board 20 minutes.
Make the jus (20 min): Set the pan on the stove, add the onion and cook 5 minutes. Pour in the wine and scrape up the browned bits, then add the stock, thyme, bay and Worcestershire and simmer 15 minutes. Strain and season.
Slice (5 min): Slice the beef very thin across the grain.
Dip (2 min per sandwich): Warm the slices for a moment in the jus. Split the rolls; dip the cut faces quickly in the jus (once for 'dipped', twice for 'double-dipped').
Build: Pile in the meat, spread with hot mustard, and serve with a pickle and a small cup of jus.
Tips
Beef on weck: brush the roll tops with egg white, sprinkle with coarse salt and caraway and bake 5 minutes; serve with fresh horseradish.
Don't let the roll soak; a quick dip keeps the crust.