Start by preheating the oven to 200 degrees Celsius (392 degrees Fahrenheit), fan-forced.
Peel the onions and garlic and chop them finely.
Put all the chopped onions in a pot and sauté them in a bit of butter.
Add the chopped beef to the pot and brown it with the onions.
Peel the carrots and celeriac and grate them on the coarse side of the grater. Add them to the pot along with the tomato paste, red wine, water, vegetable stock, and thyme and basil.
Let it simmer for 5 to 10 minutes. Then season to taste with freshly ground salt and pepper.
Grease an ovenproof dish with a bit of oil or butter and pour the meat sauce into the dish.
Pour the root vegetable mash over the meat sauce and spread it out evenly.