Put the dried beans in a saucepan and cover them with cold water (for 100 g of beans you will need about ½ a litre). Add the garlic, sage, olive oil and salt, and then put the saucepan on the stove over a very low heat (if necessary, reduce the heat even more while cooking). The water should boil, but imperceptibly; the beans mustn’t be “agitated”, in fact they should hardly move. It’s not easy to give a precise cooking time, it depends on the type of beans and on their “age”... but don’t worry, there’s a solution that’s always valid when cooking: taste them! Wash the prawns well and then put them in boiling water, with a pinch of coarse salt; when the water returns to the boil, cook them for 5 minutes and then strain them. Wash the tomatoes, peel them and remove the seeds. Now chop them and leave the pieces in a colander so the water drains off. Clean the onions and put them in water to soak for half an hour, changing the water at least once (this makes them more digestible and decreases their “odour” in the mouth); then chop them. When the prawns have cooled down a little, peel them and put them in a salad bowl with the chopped tomatoes and onions, and the well drained beans. Add the olive oil, chilli pepper, basil leaves, vinegar and some salt. Mix delicately, taking care not to squash the various ingredients. This mouth-watering salad can be served while still slightly warm, or you can keep it in the fridge and serve it cold, as an appetizer or a main course, especially in the summer.