1To make the mashed potato Place the potatoes in a large saucepan and cover with cold water, add a good pinch salt. Cover and bring to the boil over high heat. Reduce heat to medium-low. Cook, partially covered, for 10 minutes or until potatoes are tender. Drain and return the potatoes to hot saucepan. Roughly mash. Add the butter and milk. Beat with a wooden spoon until creamy. Season with salt and pepper. Cover and keep warm.
2Meanwhile, heat oil in a large, deep frying pan over medium-high heat. Add the onion. Cook, stirring, for 2 minutes or until soft. Increase heat to high. Add the mince. Cook, stirring constantly to break up mince, for 5 minutes or until browned.
3Add the mushrooms, tomato paste, tomatoes, stock and Worcestershire sauce. Cook, stirring occasionally, for 15 minutes or until sauce has thickened. Taste and season with salt and pepper.
4Preheat oven to 220°C. Spoon mince mixture into a 5-cup capacity ovenproof dish. Top with mashed potato. Bake for 15-20 minutes or until potato begins to turn golden. Serve.