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1
Preheat the oven to 350.
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2
In a food processor, pulse the graham crackers with the granulated sugar and cinnamon until finely ground.
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3
Add the butter and pulse until the crumbs are evenly moistened.
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4
Press the crumbs into the bottom and up the side of a lightly buttered 9-inch glass pie plate.
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5
Bake for 10 minutes, until the crust is lightly browned.
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6
Transfer the crust to a rack to cool completely.
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7
Poke the sweet potatoes all over with a fork and microwave at high power for about 5 minutes, until just barely tender.
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8
Transfer the potatoes to the oven and bake for about 10 minutes, until they are tender; let cool.
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9
Scoop the flesh into a food processor and puree until smooth.
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10
In a small bowl, sprinkle the gelatin over the 1/4 cup of water and let stand until softened.
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11
In a medium saucepan, heat the half-and-half just until small bubbles appear around the edge; cover and keep warm.
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12
Meanwhile, in a medium heatproof bowl, using an electric mixer, beat the egg yolks at high speed until thick, about 3 minutes.
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13
Add 1/4 cup of the granulated sugar and beat until very thick, about 5 minutes.
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14
At low speed, gradually beat in the warm half-and-half.
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15
Fill the saucepan with 1-inch of water and bring to a simmer.
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16
Set the bowl with the egg yolks over the simmering water and cook, stirring constantly, until thickened and an instant-read thermometer inserted in the yolks registers 170, about 9 minutes.
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17
Add the softened gelatin to the custard and cook for 1 minute, stirring until dissolved.
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18
Remove the bowl from the pan.
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19
Stir in the pureed sweet potatoes, 2 teaspoons of the vanilla, the pumpkin pie spice and the salt.
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20
Put the egg whites and the remaining 1/4 cup plus 2 tablespoons of granulated sugar in a medium heatproof bowl.
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21
Set the bowl over the simmering water and cook, stirring, until an instant-read thermometer inserted in the whites registers 160.
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22
Remove the bowl from the pan and using clean beaters, beat the egg whites at high speed until stiff and glossy.
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23
Using a large rubber spatula, fold the egg whites into the custard until no streaks remain.
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24
Pour as much of the custard into the pie crust as will fit (there will be some left over) and refrigerate until the top is just set, about 15 minutes.
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25
Spoon the remaining custard on top and refrigerate the pie until very cold and firm, at least 8 hours.
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26
In a medium bowl, using an electric mixer, beat the heavy cream with the confectioners' sugar and the remaining 1/2 teaspoon vanilla at medium-high speed until firm.
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27
Spoon the whipped cream over the pie, dust with cinnamon and serve.
