Prepare the Plantains

1. Peel the plantains by cutting off the ends and making a slit along the skin. Use your fingers to peel off the skin.
2. Cut each plantain into three pieces.
3. In a pot, cover the plantains with water and add a pinch of salt. Bring to a boil and cook until the plantains are very tender but not falling apart (about 20-25 minutes).

Cook the Onions

1. While the plantains are boiling, slice the onion thinly.
2. In a small saucepan, cook the onion slices over medium heat with 3 tablespoons of water and the white vinegar. Stir occasionally.
3. Cook until the onions become translucent, about 7 minutes. Remove from heat and set aside.

Mash the Plantains

1. Once the plantains are tender, drain them and place them back in the pot.
2. Add the olive oil or butter to the plantains.
3. Mash the plantains with a fork until smooth. If the plantains are too dry, add a little warm salted water until the desired consistency is achieved.

Serve

1. Serve the mashed plantains on a plate.
2. Top with the cooked onions and garnish with fresh cilantro if desired.
3. Serve warm and enjoy!