Transfer the Apple and onion filling to a blender bowl, add the mustard, 10 tbsp of water or broth, and a pinch of salt. Puree into a homogeneous mass. You can add more water if you want a more liquid sauce. Heat the pan well, add the butter and a drop of olive oil. Over high heat, fry the steaks on both sides until browned. Then reduce the heat, pour in 50 ml of water or broth and simmer the meat with the lid closed until tender. Focus on what kind of roast meat you like. I like well-done meat. Serve the finished meat with fresh vegetables and herbs, plentifully watering the meat pieces with sauce.