Preheat the oven to 400 degrees F. Pierce the sweet potatoes 2 or 3 times with a fork. Put on a baking sheet and roast until very tender and a knife easily pierces through the center, 45 to 60 minutes.
Let the potatoes cool slightly and then halve lengthwise. Holding the sweet potatoes with a potholder or towel, scoop out the insides and discard the skins. Pass the potatoes through a food mill or ricer into a large bowl.
Heat the butter, maple syrup and zest in a small skillet over medium heat until the butter is melted. Pour over the potatoes and stir to combine evenly. Season with salt and pepper.
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