Bring a large saucepan of water to the boil. Peel the potatoes, then add to the pan and simmer until tender.
Meanwhile, heat the olive oil in a pan and fry the onion and garlic until soft. Add the mince and cook until browned.
Add the mustard, chopped tomatoes and the herbs, then simmer for 15 minutes.
Preheat the oven to 180°C, fan 160°C, gas 4. Mash the potatoes with the butter and a little milk to create a smooth mash.
Place the beef mixture in an ovenproof dish, then top with the mashed potato, covering the beef evenly. Bake for 25 minutes.
Meanwhile, steam or boil the carrots until tender. Season and serve with the cottage pie.