Turn the slow cooker on to low to pre-warm while preparing the ingredients. To make the stuffing, mix together the breadcrumbs, butter, celery seeds, thyme, oregano and lemon rind. Place one schnitzel on top of a piece of damp plastic wrap on a chopping board. Sprinkle the meat with a little water and cover with a second sheet of plastic wrap. Hit firmly with a mallet or rolling pin to flatten the schnitzels so they are an even thickness. The dampened plastic will help prevent the meat from tearing. Cut the schnitzels in half cross-wise. Place a spoonful of stuffing on each piece of beef and roll up to enclose the filling. Secure with a toothpick. If wishing to brown the ingredients: Heat a dash of oil in a frying-pan and fry the beef olives until well browned. Brown the onion if wished. Put the beef olives, onion and prunes into the pre-warmed slow cooker. In a jug, mix together the flour, stock, redcurrant jelly if using and HP or Worcestershire sauce, and pour over the beef olives.
Cover with the lid. Cook on low for 6–7 hours or on high for 3–4 hours. Serve the beef olives with seasonal vegetables. Oven Cooking Option Cook, covered in an ovenproof casserole dish in a pre-heated 1600C oven for two hours or until the meat is tender.