Place a large pan over a medium-low heat. Add the oil and, when hot but not smoking, add the onion, carrot and celery. Fry gently for 15 minutes, stirring frequently, until the vegetables are very soft

Add the lentils and stir to coat in the cooking juices. Pour over the wine and allow it to evaporate. Add roughly half of the warm stock, cover and let the lentils simmer for about 15 minutes, stirring occasionally

When the lentils have absorbed all the available liquid, add half of the remaining stock and the tomato concentrate. Stir to dissolve. Taste and decide how much longer they should go: at this point, it should be about 10 minutes

Keep adding more stock as needed (how much really depends on how liquid you like your legume soup; I like it on the denser side), and stir and taste more frequently now. Adjust the seasoning to your taste

Once the lentils are tender and the soup is dense, remove it from the heat and allow it to rest, covered, for 10 minutes

Serve with a swirl of grassy olive oil – best if from Umbria – and toasted bread