Place the potatoes in a large pot. Fill it with enough water to completely submerge the potatoes by an inch or two. Turn the heat to high and bring the water to a boil. Once boiling, cook the potatoes for at least 15 minutes or until tender enough that the potatoes can easily be pierced with a knife. Drain to potatoes and place them into an ice water bath to cool. Once cool, peel the potatoes—the skin should easily peel away.
Preheat the oven to 425°F. Place the whole, peeled potatoes into a stand mixer, fitted with a paddle attachment. Mix the potatoes on a low speed until smooth. Add the mascarpone, maple syrup, brown sugar, 1/2 of the lemon zest, 1/2 teaspoon cinnamon and the salt. Pour the mixture into the pie shell then place the pie onto a cookie sheet. Bake the pie for 15 minutes and then lower the heat to 350°F and cook for an additional 45 minutes. Remove the pie and let cool.