Either roast and char the chiles over an open gas flame (stovetop), under a broiler, or on a BBQ grill.
Roast the poblanos on stove top flame, turning them over occasionally, until skins are charred and blistered, about 10 minutes. Alternatively, you can place them on a baking sheet under an oven broiler until the skins blacken and blister. Or, place them on a hot barbecue grill and cook until the skins blacken and blister.
Transfer the poblanos into a bowl and cover with a kitchen towel, or seal in a brown paper bag to steam for 5-10 minutes. Peel the charred skin from the roasted poblano peppers and slice them into 1 inch strips.
Melt butter in a saucepan or skillet and saute onions over medium high heat until softened. Add garlic, roasted poblano slices, corn, salt, pepper and cumin. Cook for 2 minutes stirring often.
Lower heat to medium, add the cream cheese and Mexican crema. Mix well and cook for about 5 minutes or until the cream starts to bubble.
Add shredded cheese, cover the pot and turn off the heat. Let it sit covered until the cheese melts. Serve immediately with warm tortillas, tortilla chips or as a side dish (See Note 2).
Good substitutes for Oaxaca are Monterey Jack, Chihuahua or Mozzarella.
To serve as a main dish, add cooked and shredded chicken or beef.