Soak the white beans overnight, then boil for 30-40 minutes (do not salt).
Then put the beans in a colander, cool.
Add about 3 tablespoons of lemon vinegar to the beans. Leave for 30 minutes, you can put it in the refrigerator.
Cut the onion into half rings, add salt well and add a spoonful of the same vinegar, mix and leave for 20-30 minutes.