1. Prepare the ingredients according to the list.
2. In a pan, brown the ground beef. Season it with salt and pepper. Drain the rendered fat and set aside.
3. In a pot boil the russet potatoes. Set aside.
4. Preheat the oven to 350 degrees F.
5. In a pan, heat olive oil. Add the onion, thyme and garlic. Sauté for 3 minutes till onion is translucent.
6. Put the carrot and celery. Let them cook for 2 minutes.
7. Add the tomato paste and some stock. Mix them well and let the vegetable cook for 7 minutes.
8. Put the beef into it and pour the remaining stock. Mix well. Allow it to simmer for 20 minutes.
9. In the meanwhile, in a large bowl, take the boiled potatoes with a little boiling liquid. Put butter and mix well.
10. Pour milk little at a time and mash the potatoes. Keep adding milk as required. Do not over beat the potatoes to keep them soft. Set aside.
11. Take a baking dish. Layer it with a layer of mashed potatoes at the bottom.
12. Place the cooked beef and vegetables on it and cover it with another layer of mashed potatoes.
13. Bake it in the oven for 25 minutes or till the potatoes begin to turn golden brown.
14. In a serving plate, ladle some pie and serve hot with green salad.