Wash, clean and chop the beans. Simmer with a little salt water for about 20 minutes. Peel the onions, cut into slices and fry in the oil until translucent. When they are done, dust the curry over them, stir in and fry briefly. Add the onions to the hot beans, mix carefully with the sugar and hot stock, bring to the boil again. Mix the cornstarch with the vinegar and bind the vegetables with it.