For the pecan crust:
For the pecan crust, preheat the oven to 350 ºF (180 ºC). Stir the graham cracker crumbs, pecans and melted butter together until evenly combined and press this into a lightly greased 9-inch (23 cm) pie plate. Bake the crust for 10 minutes, and then cool while preparing the filling.
For the maple pecans:
Keep the oven at 350 ºF (180 ºC). Line a baking tray with parchment paper. Toss the pecan halves with the maple syrup, salt and cinnamon to coat and spread these in an even layer on the baking tray. Bake the pecans for about 10 minutes, stirring once halfway through cooking, until they are toasted. Once the pecans cool, the maple syrup will harden on.
For the filling:
For the filling, reduce the oven temperature to 325 ºF (160 ºC). In a medium saucepan, bring the maple syrup to a boil and boil for 2 minutes (to reduce it and concentrate the flavor.). Remove the pan from the heat and whisk in the butter until it has melted. Whisk in the cream and check that the mixture has cooled to at least just above room temperature (set aside a few minutes if too warm.) Whisk in the egg yolks, whole egg and vanilla and pour this into the cooled pie shell. Bake the pie for about 40 minutes, until it is set around the edges but still has a little jiggle just in the center. Let the pie cool to room temperature, and then chill it for at least 4 hours before topping.
For the toppng:
Whip the cream until it holds a soft peak and fold in the maple syrup, milk powder and vanilla. Dollop and spread this on top of the cooled pie. Chopped the maple pecans and sprinkle these on top. The pie can be served immediately or chilled until ready to serve, up to 8 hours ahead.