To make the meat sauce, heat the oil in a large, deep frying pan. Add onion, garlic, carrot and celery and cook over a medium-high heat, stirring often for 8 minutes, until vegetables soften slightly. Add tomato paste. Cook, stirring for 2 minutes. Increase heat to high, add the mince and cook, stirring with a wooden spoon to break it up for 5 minutes, or until the mince changes colour.
Stir in the tomatoes, oregano, stock cube and water. Season with pepper and bring to the boil. Reduce heat to medium-low, cover and simmer, stirring occasionally for 20 minutes. Remove the lid and simmer uncovered a further 5-10 minutes, or until sauce has reduced and thickened. Taste and season with more pepper, if needed.
For the potato mash, place potatoes in a saucepan, cover with cold water. Cover with lid and bring to the boil. Reduce heat and gently boil for 15 minutes or until tender. Drain well then return to the hot pan. Mash well. Add milk and beat until smooth. Season with pepper.
Preheat oven to 220C (200C fan-forced). Spoon the meat sauce into one, 6-cup capacity ovenproof dish, or four 1 1/2 - cup capacity ovenproof dishes. Top with mashed potato. Brush with olive oil. Bake for 20-30 minutes or until piping hot. Serve with steamed beans.

Image credit: Ben Dearnley Photography