Dice the onion and mince the garlic. Finely chop the carrots and celery stick.
Heat the oil in a large skillet and sautee the onion for 2 minutes. Add the garlic and cook 1 minute more.
Bring in all the veggies and cook for about 5 minutes, to soften.
Add the minced beef and use a wooden spoon or spatula to break it. Stir well to combine. Cook until the meat is no longer pink.
Add the tomato paste, flour and dried herbs. Pour the vegetable stock and bring to a boil.
Reduce the heat to low, cover with a lid and simmer for 10 minutes. After the cooking time, the mince mix should have a thicker consistency and not too much liquid.
Season with salt and pepper, to taste.
Meanwhile, peel the potatoes and chop into smaller pieces. Place them in a pot, cover with water and boil until they are tender, for about 20 minutes. You may prick with a fork to check if they are cooked.
Drain and use a fork or a potato masher to crush them. Add the butter, milk, Cheddar cheese and nutmeg. Mix until well combined and creamy. Adjust the taste for salt.
Preheat the oven to 400F.
Spoon the mince mixture onto a large baking dish. Level it up.
Add the potato mash on top and use a spatula to smooth it. Make some lines with a fork so you will have a crispy top after it is baked.
Place the dish in the oven and bake for about 25 minutes or until the top is golden-brown.
Serve it warm and enjoy!