Put the potatoes in a large pot with 2 tablespoons of salt and cover by a few inches of cold water. Bring to a boil, cover and cook until a paring knife inserted in the center meets no resistance.
Meanwhile, heat 2 tablespoons of the butter in a medium saucepan over medium heat. Whisk in the flour and cook 1 minute. Whisk in the hot milk and increase the heat to high, cooking until the milk has thickened and the flour taste has been cooked out, about 5 minutes. Remove from the heat and whisk in the Monterey Jack cheese until smooth and melted. Stir in the Parmigiano-Reggiano and poblano chile and season with salt and pepper.
Drain the potatoes well, and then return to the pot over low heat to dry out. When the potatoes turn white and become dry, pass them through a ricer into a large glass bowl. Gently combine the potatoes with the remaining 6 tablespoons butter and the warm cream, using a wooden spoon. Season with salt and pepper.
Make a well in the middle of the potatoes and fill with the cheese sauce. Garnish with cilantro and serve.