1. Tear the bread into small chunks, place into a large bowl with 2 tbsp milk and set aside for 10 minutes. Using your hands, mix the milk-soaked bread, beef mince, carrot, grated onion, egg, mustard (if using), salt and pepper until very well combined. Shape the mixture into 4 patties, then refrigerate for 10 minutes to firm. Preheat your oven to 75°C.  

2. Place a large frying pan over a medium-high heat and add the oil. Fry the patties until cooked through, about 4 minutes on each side. Remove from pan and transfer to the oven to keep warm while you prepare the gravy. Slice the mushrooms and the remaining onion.

3. Melt the butter in the same pan used to cook the patties. Cook the onion and mushrooms over a medium heat until golden and the liquid has evaporated from the mushrooms, about 6 minutes. Add the flour and cook for 1 minute, stirring constantly. Gradually pour in beef stock, water, tomato sauce and soy sauce, stirring frequently.

4. Cook until thickened, about 5 minutes. Season to taste with salt and pepper. Return the patties to the pan and coat in the gravy. Place each patty on a plate and spoon the remaining gravy over the top. Serve with mashed potato and boiled peas.