Wash potatoes and cut into 2-inch pieces. Place in a large saucepan and add cold water to cover. Cover with a lid and boil until potatoes are tender. While potatoes cook, heat olive oil over medium heat in a medium non-stick skillet. Saute onion, garlic and jalapeno pepper 10 minutes. Drain potatoes and mash with a potato ricer or in the food processor fitted with the plastic blade. With a fork, combine the potatoes with the onion mixture. Add sour cream and cilantro and mix well. Add salt and pepper to taste.