½ cup (1 stick) cold unsalted butter, cubed and chilled again
¼ cup ice water
For the filling:
1½ pounds (2 very large or 2 medium) yams, or 2¼ cups pre-cooked mashed yams
¾ cup sugar
½ cup sweetened condensed milk
¼ cup light brown sugar
1 tablespoon vanilla extract
½ teaspoon ground cinnamon
¼ teaspoon fine salt
For the streusel:
1 cup pecans
¼ cup firmly packed dark brown sugar
3 tablespoons cubed unsalted butter, chilled
3 tablespoons all-purpose flour
½ teaspoon ground cinnamon
⅛ teaspoon fine sea salt
Make the pie crust Pulse the flour and sea salt in a food processor until incorporated. Add the chilled butter and pulse until pea-sized pieces of butter remain, 15-20 pulses. Add the ice water and pulse until a dough just forms, 15-20 pulses. On a floured surface, gather the dough into a 5-inch disc, wrap in plastic wrap and chill for at least 30 minutes (you can keep the dough in the fridge for up to 2 days). Using a floured rolling pin and on a floured surface, roll the disc into a 12-inch circle (it doesn’t have to be perfect). Fit the dough into a 9-inch pie plate, trim the edges to leave a 1-inch overhang, then tuck the edge under itself to form a thicker crust. Use a fork or your fingers to crimp into a pattern.Chill while you make the filling.
Make the filling Preheat the oven to 375°F. Prick the yams with a fork and wrap in foil. Bake until the yams are tender, about 1 hour. Remove from the oven (leave the oven on), open the foil, and cool until easy to handle. Split the yams and scrape out the filling into a bowl (discard the skins); cool for another 10 minutes (you should have between 2 and 2¼ cups mashed yams). Add the sugar, condensed milk, brown sugar, eggs, vanilla, cinnamon, salt, and a dash of nutmeg and whisk until smooth.
Make the streusel Toast the pecans by placing them in a dry skillet over medium heat and cooking them, tossing or stirring often, until fragrant, 5-6 minutes. Transfer to a plate to cool, then chop and combine in a bowl with the brown sugar, butter, flour, cinnamon, and salt. Using your fingers, pinch the streusel together until it is uniformly clumpy.
Bake the pie Raise the oven temperature to 400°F. Take the crust out of the fridge, pour the filling into the crust, and bake for 20 minutes. Open the oven and carefully sprinkle on the streusel topping. Reduce the heat to 350°F and continue to bake until the pie is just set and streusel is golden and crisp, 20-25 minutes. Remove from the oven and set on a trivet to cool.
Make the whipped cream While the pie is baking, combine the cream, vanilla bean or extract, and sugar in a large bowl and whisk until soft peaks form, 3-4 minutes. Serve the whipped cream with the pie.