Preheat the oven to 350 degrees F. Line a sheet pan with aluminum foil.
Place the sweet potatoes on the prepared sheet pan and pierce each potato 4 times with a small knife. Roast for 1 to 1 1/4 hours, until very tender inside when tested with a knife. Set aside until cool enough to handle. (Leave the oven on.) Peel the potatoes, discard the skins and place the potatoes in the bowl of an electric mixer fitted with the paddle attachment.
Meanwhile, place the milk, cream, chipotle chile and adobo sauce in a small saucepan. Bring to a boil, lower the heat and simmer for 5 minutes. (It might look curdled.)
With the mixer on low speed, add the chipotle-milk mixture to the sweet potatoes. Add the maple syrup, butter and 1 tablespoon salt. Mix until the potatoes are coarsely pureed. Pour into a 9-by-12-by-2-inch oval oven-to-table baking dish and bake for 30 minutes, until heated through. Sprinkle with salt and pepper and serve hot.
Make ahead: Prepare the sweet potato mixture, spoon it into the baking dish, cover and refrigerate for up to 3 days. Bake at 350 degrees F for 40 to 45 minutes, until hot.