Mince or cut the meat into dice. Melt the butter in a saucepan and fry the finely-chopped onion until lightly browned. Sprinkle in the flour and brown slightly, then add the gravy or stock and boil for 2–3 min. Add the meat, ketchup, sauce or vinegar, season with salt and pepper, and keep hot without boiling for 10–15 min. Meanwhile poach the eggs and cut the toast into small triangles. Turn the mince on to a hot dish, place the eggs on top and place the pieces of toast round the base.