1 small onion, chopped
leftover gravy
175g/6oz plain flour
pinch of salt
40驳/1陆辞锄 butter
1 tbsp oil or butter
1 free-range egg, beaten with a drop of milk
40驳/1陆辞锄 lard
1 thick slice bread
125驳/4陆辞锄 roast beef, or other cooked meat