Butter a 23 cm (9 in) tart pan with a removable bottom. Preheat the oven to 160°C (325°F).
For the pecan crust
In a bowl, combine the pecans, maple sugar, flour, allspice, and salt. Add the melted butter and mix with a fork until the dry ingredients are moistened. Transfer the mixture to the prepared tart pan.
Press the mixture firmly to the bottom and sides of the pan to form the crust. Bake for 15 minutes, or until the crust is aromatic and just starts to brown. Remove from the oven and set aside.
For the filling
In the bowl of a stand mixer, combine all of the filling ingredients until the mixture is light and smooth. Pour the filling into the crust and use a spatula to smooth out the top of the tart. Bake until the filling is set, 60 to 75 minutes. Once done, the filling should still look moist but not soft. The filling will firm up some more as the tart cools.
Place the tart on a wire rack and let cool to room temperature, then refrigerate for at least two hours.
Gently unmold the tart to avoid damaging the crust. Garnish with whole pecans and whipped cream, and serve.