In a cast iron pot bring 6 cups of water, sea salt, kombu to a boil, then add peeled plantains. Each plantain should be cut in half.
Boil for ~20-25 minutes or until soft.
*Do not throw the away the water used for boiling plantains!
Remove plantains from water and into a bowl then add cold water and olive oil and mash until you reach a smooth consistency. You can use a mashed potato masher or fork.
Onion preparation
Heat ¼ cup boiled plantain water, olive oil, and raw apple cider vinegar in a frying pan, then add onions
Cover and bring to a simmer for about 2 minutes. You will notice the onions will become translucent.
Serve over mangu.
Recipe by Eileen Z. Fuentes at http://www.eileenzfuentes.com/2012/04/mangu-2-0/