For the crust: Place pecans in a food processor and process until finely ground. Add the flour, salt, black pepper and the rest of the spices and pulse to combine.Add the the cold butter and pulse until pieces of butter are well frostbites and pea sized. Add the ice water and pulse a few times until loose dough forms. Empty out onto a lightly floured surface, form the dough into a disc, wrap in plastic wrap and chill in the fridge for at least an hour or preferably overnight.For the sweet potato filling: Preheat oven to 350°F. Place the sweet potatoes on a parchment-lined sheet tray and roast until tender, about 1 hour. Remove from the oven; let cool. Peel and scrape out the flesh, discarding the skin. You should have approx 2 cups of cooked sweet potatoes.Transfer the sweet potatoes, along with the remaining filling ingredients, into a food processor and purée until smooth; set aside.Remove the dough from the refrigerator and transfer it to a floured work surface. Using a rolling pin, roll the dough out to an ⅛-inch thick. Transfer the dough to a 9-inch nonstick pie pan (or a lightly greased one) and trim excess dough around the edge of the pan, fold edges under and crimp edges of the crust decoratively. Poke a hole in dough at the bottom of the pan using a fork and chill in the fridge for 20 minutes.Remove the dough from the fridge. Place a large piece of parchment or foil over the pie dough and fill with dried beans, rice or sugar (to weigh down the crust).Bake dough until fragrant and light golden brown, about 8 minutes. Remove the dough and discard the beans and parchment; let cool. Brush edges of crust with egg wash and sprinkle turbinado sugar over edges.Pour the sweet potato mixture into the pie and bake until the filling is just set, about 45 minutes. Transfer to a wire rack and allow to cool completely before slicing, about 2 hours. Serve with whip cream. Cover leftovers tightly and store in the refrigerator for up to 5 days.