• Prepare the pastry and line a 9-inch pie pan. Trim the dough and crimp the edges as desired. Place the pie shell in the refrigerator for 60 minutes. This will help control shrinkage during the blind bake.
• Preheat oven to 425°F. Line the chilled pastry with two sheets of heavy-duty foil, then fill with 2 cups dried beans or pie weights. Bake for 20 minutes. Remove the foil, beans or weights and return the pastry to the oven. Bake until light golden brown, about 10 minutes longer. Remove from the oven and reduce the oven temperature to 350°F.

To make the pie filling:

• Prick the sweet potatoes with a fork and place on a double layer of paper towels in the microwave. Cook at full power for 5 minutes then turn each potato over and cook another 5 minutes or until tender, but not mushy. Cool the potatoes for 10 minutes then cut each one in half crosswise. Scoop out the flesh with a spoon and transfer to a medium mixing bowl. Discard the skins. You should have 2 cups of flesh. Add 2 tablespoons butter and mash with a fork while the potatoes are still warm. A few small lumps of potato are fine.
• In a medium mixing bowl whisk together the egg yolks, egg, sugar, maple syrup, salt, allspice, nutmeg, cinnamon vanilla and buttermilk. Add the egg mixture to the sweet potatoes and fold together gently with a rubber spatula until combined.
• Place the pie crust on a foil lined baking sheet. Pour the sweet potato filling into the pie crust. Use little strips of foil to create a collar and shield the edges of the crust to prevent over-browning. Bake for 40 minutes.
• After the pie is in the oven for 30 minutes, make the praline topping. In a small saucepan melt the butter over medium heat. Stir in the brown sugar, maple syrup and milk. Cook, stirring constantly, until the mixture comes to a boil. With the pie still in the oven remove the foil from the around the edge of the crust. Sprinkle the pecans over the partially baked pie then carefully pour the hot brown sugar mixture over the pecans. Bake for another 15 to 20 minutes or until the center of the pie appears set when shaken.
• Cool on a wire rack for at least 1 hour. Cover and refrigerate until ready to serve. Pie keeps up to 4 days.