Preheat oven to 425°.
In a small bowl, whisk the sugars with the spices and salt.
In a medium bowl, whisk the eggs, then whisk in the sugar mixture into the egg mixture.
Add the pumpkin puree and evaporated milk and whisk until smooth.
Pour mixture into a prebaked crust and bake for 10 minutes.
Lower temperature to 350° and bake for about 25 minutes longer, until the filling is fully set.
Transfer to a wire rack and let cool completely.
Cut into bars and serve with whipped cream.