For the steamed onion roast, cut the roast beef into 4 slices. Pat and cut the edges.
Salt, pepper, coat one side with mustard and rub.
Cut the onions into fine strips. Heat the oil, place the roast with the mustard side down and brown.
Turn and lift out of the pan.
In the remaining fat, brown the onions, dust with flour and fry until heated through. Add soup or water and season.
Steam the roast for about 1 hour and 15 minutes until tender. Arrange the roast onion and serve.