Preheat the oven to broil on high and place a rack in the highest position.
Remove stem, seeds, and ribs from the poblano peppers. Cut the pepper into large pieces that will lay flat on a baking sheet. I do this by cutting off the top, then cutting the body of the pepper into about four large chunks. You can press down on any pieces sticking up and it should crack the pepper enough to flatten it out. You just don't want any pieces sticking up a lot higher than the rest of them.
Broil the flattened peppers skin-side up until blistered and charred, about five minutes. Immediately transfer the peppers to a bowl and cover tightly with plastic wrap. Allow the peppers to steam for about ten minutes. The skin should peel off easily. Remove the skin from the peppers. It's ok if a few bits remain.
When you take the peppers out of the oven, lower the rack to the middle position and preheat the oven to 375ºF. Coat a 9x13 baking dish with cooking spray and set aside.
Place the roasted peppers in a food processor along with the onion, cilantro, garlic, heavy cream, and sour cream. Process just until smooth.
In a 2 quart saucepan, heat butter over medium heat until melted. Whisk in flour and cook, whisking, for one minute. Add the poblano mixture and cook for a few minutes, whisking frequently. Add vegetable stock and 1/2 cup of Monterey jack cheese. Let cook 5-10 minutes, stirring frequently.
To prepare the filling, combine beans, corn, 1 cup Monterey jack cheese, cumin, coriander, and 1/4 cup of the cream sauce in a large bowl. Divide filling evenly amongst tortillas, placing a spoonful in a line across the center and rolling it tightly. Place filled tortillas seam side down in the prepared baking dish. Cover completely with the remaining cream sauce and sprinkle with remaining cheeses.
Bake 20-25 minutes or until bubbly and beginning to brown.