1. Place the mince in a non-stick frying pan and cook over a medium heat, stirring until beginning to brown.
2. Meanwhile, peel and chop the onion and carrot into 1cm cubes. Add to the mince and cook for 2 minutes.
3. Make up the stock cube with 125ml of boiling water from the kettle. Add the flour to the mince, stir well for 1 min. Add the stock, with the tomatoes and herbs and bring to the boil, stirring. Cover and cook for 10mins. Add the peas, then simmer for a further 5 minutes or until the mince and vegetables are tender.
4. Meanwhile, peel the potato and cut into large chunks. Cook in boiling water for 10 minutes or until tender. Drain then mash with the butter.
5. Divide the mince over the base of four small ovenproof dishes, then top with the potato. If eating straight away, pop the pie under the grill until the top is brown if liked. If serving later, cool, then chill. Bake at 180ºC for 20-25mins or until piping hot - cool before serving.