Cream of Poblano Chile and Potato Soup

Roast the chiles directly over a gas flame or under a preheated broiler, turning frequently with tongs, until charred all over, about 3 to 4 minutes.
Watch carefully to prevent charring too much or the chiles may get too soft.
Place in a plastic bag and steam about 5 minutes.
Wearing rubber gloves, rub or scrape off the charred skin.
Cut the chiles open, remove the seeds and veins.
Chop coarsely and reserve.
In a large heavy saucepan, heat the butter and oil over medium heat.
Cook the onion and garlic, stirring frequently, until softened, 3 to 4 minutes.
Add the potato, water, parsley, and chicken stock.
Bring to a boil, then reduce the heat to medium-low and cook until the potato is very tender, about 15 minutes.
Meanwhile, bring a small pot of water to a boil and cook the corn until just tender, about 3 minutes.
Drain and reserve.
When the potato is done, transfer the contents of the saucepan to a blender or food processor.
Add the reserved chiles, cream, and salt.
Purée until smooth.
Return the soup to the saucepan, and bring to a boil over medium-low heat, stirring frequently, to prevent scorching.
Divide the soup among 4 soup bowls.
Garnish each serving with about 2 tablespoons of corn, and sprinkle with parsley.