Cut potatoes into 1/2 inch cubes and place in saucepan with cold water and bring to a simmer. Cook until potatoes are tender, about 30-40 minutes. Place potatoes in a large bowl with yogurt, salt, pepper, and olive oil. Mash potatoes until smooth with a large spoon or hand mixer. Chop parsley and sprinkle on potatoes. Drizzle a few drops of olive oil on potatoes if desired.