Soak the beans for at least 12 hours; strain them and put them to boil in a saucepan full of cold water over a low heat, for roughly an hour, with 2 sage leaves, the clove of garlic without its skin, 1 spoonful of olive oil and a pinch of salt (this latter added at the end of cooking). Finely chop the onion, put it in a heavy-bottomed pan with the olive oil and let it soften over a moderate heat. Dice the celery, slice the carrot and put them all in the pan with the onion, stirring well. Add the tomato passata, season with salt and, if you like, some freshly ground pepper or hot chilli pepper, and stir thoroughly. When the beans are cooked, put more than half of them (with a ladle or 2 of the water they were cooked in) through a food mill. Put the bean purée back on the stove in a pan with the whole beans, the remaining water they were cooked in and the uncooked spelt. Cook over a low heat for roughly an hour; stir the soup frequently and take care that it doesn’t stick to the bottom of the pan, it’s fairly thick. When it’s cooked, taste the soup and add a little salt and pepper, or chilli pepper, if necessary. Wait about an hour before serving, it will have amalgamated better and be delicious. If any is left over, it’s also very good the following day.