Onions and beans beef tendons

PREPARATION

Wash the tendons well. In a large saucepan, boil plenty of water with a tablespoon of vinegar and a pinch of salt. Once you have reached the boil, add the tendons, cover and cook over a moderate flame until it is easy to cut them with a knife. Drain and cut into chunks, placing them in a large bowl.
Slice the onions thinly and pour over half a teaspoon of sugar to reduce the acidity. After ten minutes wash them under a jet of water, let them drip and add them to the tendons. Add boiled beans, extra virgin olive oil, vinegar, pepper and a little salt. Mix and let it rest.
The dish can be tasted as lukewarm or even cold.