Remove the skin from the onions and cut into rings. Beat the steaks, season with salt, pepper and marjoram. Then coat the meat slices with mustard. Layer the steaks in a sealable container.
Start with the onion rings, top with 2 to 3 slices of meat, drizzle the meat with oil and repeat with onion rings. Finally, pour the beer over everything.
The meat must be completely immersed in the beer.
Leave the grilled meat to stand for about 24 hours. Remove the onion rings and the meat from the beer. Steam the onion rings in a frying pan, stirring the onions a few times. Roast the roast brisket on the roasting rack (broiler), extinguishing it from time to time with the beer broth.
Put the roasted onion rings over the grilled meat. Serve with a colorful potato salad or fresh farmhouse bread and a cold beer.