How to make it
Preheat the oven to 180°C.
Heat the oil and butter in a 4L casserole dish, add the onion, celery and carrot. Cook at low heat for about 15 minutes to release all of the sweetness from the vegetables.
Add the meat and turn up the heat slightly, cook until browned all over.
Add the liquid, oyster sauce, mustard and tomatoes, and bring to the boil. Take off the heat when boiled and lay the sliced potatoes over the top, season each layer with a little of salt and pepper.
Place the casserole dish into the oven and cook for one hour. The potatoes should be golden brown on top and cooked through.