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1
Make the filling: Preheat oven to 400F.
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2
On a parchment-lined rimmed baking sheet, bake potatoes until tender, 60 to 75 minutes.
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3
Let stand until cool enough to handle.
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4
Reduce heat to 375F.
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5
Peel potatoes, and press through a ricer into a large bowl (you should have about 1 cup); let cool completely.
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6
Stir in ground ginger, vanilla, salt, egg yolks, and brown sugar.
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7
Meanwhile, in a medium saucepan, warm milk and fresh ginger over medium heat until just under a boil.
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8
Remove from heat; let stand 30 minutes.
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9
Pour through a fine sieve into a bowl and discard solids.
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10
In a saucepan over medium-high, melt butter.
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11
Whisk in flour; cook, whisking, 1 minute.
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12
Whisk in ginger-infused milk.
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13
Bring to a boil.
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14
Reduce heat to medium; cook 1 minute.
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15
Stir into potato mixture.
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16
Make the crust: Butter a 9-inch springform pan, and place on a parchment-lined rimmed baking sheet.
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17
Stir together 1/3 cup granulated sugar and 1/2 teaspoon cinnamon in a bowl.
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18
Brush 1 phyllo sheet with some melted butter.
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19
Sprinkle lightly with cinnamon-sugar mixture.
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20
Fold in half crosswise; brush with butter.
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21
Sprinkle lightly with cinnamon-sugar mixture, and fit into prepared pan, folded side in, allowing a 2 1/2 inch overhang.
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22
Repeat with each sheet, overlapping to cover bottom.
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23
With an electric mixer on high, whisk egg whites until foamy.
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24
Add cream of tartar; whisk until soft peaks form.
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25
With machine running, gradually add 1/4 cup granulated sugar; whisk until stiff glossy peaks form.
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26
Whisk one-third of egg whites into potato mixture.
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27
Using a wide flexible spatula, gently but thoroughly fold in remaining egg whites.
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28
Pour filling over phyllo; fold overhang over filling.
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29
Sprinkle with cinnamon-sugar mixture (if needed, combine 1 to 2 tablespoons more sugar with a pinch of cinnamon).
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30
Bake pie until puffed and just set in center, 45 to 50 minutes.
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31
Let pie stand until slightly cooled and center has fallen, about 20 minutes.
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32
Serve immediately.
