Preheat the oven to 325°. In a pie plate, toast the pecans for about 10 minutes, until fragrant and browned. Let the nuts cool completely.
In a food processor, combine the pecans, graham crackers, ginger, brown sugar, salt and cinnamon; pulse until crumbs form. Add the butter and process until incorporated. Press the crumbs evenly into a 9- or 10-inch pie plate. Bake the crust for about 25 minutes, until lightly browned and fragrant. Using a rubber spatula, press down the crust and let cool completely. Wipe out the processor.
Prick the sweet potatoes all over with a fork and cook in a microwave at high power for 10 minutes, until just softened. Transfer the sweet potatoes to the oven and roast for about 10 minutes longer, until soft. Let cool, then scrape out the flesh; you should have about 2 1/4 cups.
Transfer the sweet potato to the food processor and puree until smooth. Add the brown sugar, eggs and bourbon and process until blended. Add the heavy cream and process until incorporated. Pour the filling into the crust and bake for about 50 minutes, until set and the top looks dry; cover the crust edges with foil if they darken. Let the pie cool completely. Preheat the broiler.
In a small saucepan, combine the granulated sugar and water and bring to a boil. Cook over high heat without stirring until a candy thermometer inserted in the syrup registers 240°, about 5 minutes. Meanwhile, in the bowl of a standing mixer fitted with the whisk, beat the egg whites with the salt until soft peaks form. With the machine on, carefully drizzle in the hot syrup and beat at high speed until the whites are stiff, glossy and warm to the touch, about 5 minutes. Beat in the vanilla.
Mound the meringue over the sweet potato filling, swirling it decoratively. Broil the pie 4 to 6 inches from the heat for about 30 seconds, until the meringue is lightly browned. Cut the pie into wedges and serve.