Preheat the oven to 200°C/180°C fan
Spread the potatoes over a large baking tray and drizzle with 2 tbsp of olive oil and the melted butter. Season with a little salt and roast on the top shelf of the preheated oven for 25-30 minutes.
While the potatoes are roasting, heat the remaining oil in an ovenproof casserole and fry the onions, carrot, celery and venison mince for 5-8 minutes until brown.
Stir in the flour and cook for 2 minutes, stirring continuously, and then add the stock, tomato purée, Worcestershire sauce and two thirds of the parsley. Cook uncovered in the oven for 15-20 minutes.
When the potatoes are cooked, remove from the oven along with the mince. Scatter the potatoes over the mince and decorate with the remaining parsley.
Serve immediately.