Preheat the grill or a broiler to medium high heat.
Grill or broil the poblanos until the skin begins to blacken, 5 to 7 minutes. Transfer to a bowl, cover with plastic wrap, and let steam until the skin loosens, about 10 minutes. Peel the poblanos and coarsely chop. Set aside.
Add the potatoes to a small saucepan with enough water to cover, and cook until tender, 15 to 20 minutes. Drain and set aside.
Heat the oil in a large saucepan over medium high heat, then add the cumin, onion, celery and bell pepper, and sauté until the vegetables are softened, about 5 minutes. Add the salt and corn and cook for 3 to 4 minutes longer. Stir in the poblanos, potatoes, stock, heavy cream, curry powder and 1 tablespoon of the chopped coriander, and simmer until the soup thickens, 20 to 25 minutes.
Serve hot and garnish with the remaining chopped coriander.