Pre-heat oven to180`c. Season the roast beef and seal in a preheated pan on all sides. Put the meat in the oven and cook for 30-40minutes. Once ready, allow to cool. Slice the onions into rings and set aside. In a clean bowl beat the eggs and in a separate bowl season the flour. Pass the onions through flour and then the eggs and fry them in a deep fat fryer for 2 minutes, immediately put them on a paper towel to remove any excess oil. Thinly slice the beef and again season. Now start building this sandwich by slicing the Yorkshire pudding in half. Add the roast beef or bacon, one dollop of horseradish, onions rings and finish with the rucola.