Heat pumpkin puree in a heavy pan; stir frequently.
Add milk and cream to pumpkin puree, continue heating at a medium temperature and stir until smooth.
In a heatproof bowl, beat eggs until smooth.
Beat in dry spices.
Then beat in maple syrup.
When the pie crust is baked, beat the egg mixture while pouring the hot pumpkin mixture into it in a thin stream. The resulting mixture will be hot but not so hot as to cook the eggs.
Carefully pour hot pumpkin filling into hot pie crust; return to centre of oven and bake at 400°.
The pie is done when the outside edge of the filling is firm and slightly puffed, but the centre is still jiggly. Remove to a rack and let cool gently, so the custard can first finish cooking, and then set.
Once pie has cooled top with a thin layer of cold maple syrup.
Arrange walnuts in any pattern on the pie.
Serve with a dollop of whipping cream and sprinkle of cinnamon.