Add oil to a large fry pan over high heat. Add onion, garlic, carrot and celery and fry 3-4 mins until softened. Add tomato paste and chutney, stir well. Add mince, stir well then fry 6-8 mins until browned and cooked through.
Add flour, mix well. Add stock, bring to the boil then reduce heat and cook, stirring occasionally for 20-25 mins until thickened. Season.
Preheat oven to 200ºC (180ºC fan).
Place potatoes in a large saucepan of cold, salted water. Bring to the boil then cook for 20-25 mins until soft. Drain, add milk and half the butter and mash well. Taste and season with salt according to taste.
Spoon the mince mixture into an ovenproof dish (2L capacity) then top with mashed potato, using a fork to decorate the top. Press dabs of extra butter into the potato topping then bake 20-25 mins until golden.