Peel and chop the onion and garlic.
Peel the carrot, beetroot and celeriac, then cut them into smallish chunks.
Heat the oil in a saucepan, then sauté the onion and garlic for 5 minutes.
Add the chopped vegetables, red lentils and fennel seeds, stir for a minute, then add the passata and stock.
Bring to the boil and cook for 25-30 minutes. If it’s too thick, add more stock.
When the vegetables are tender, turn off the heat. Add the dill, then process the soup until you get a smooth or textured consistency. You might need more stock for a thinner soup.