Preheat the oven to 425°. In a small bowl, whisk the sugars with the spices and salt. In a medium bowl, whisk the eggs. Whisk in the sugar mixture, then whisk in the pumpkin puree and the evaporated milk until smooth.
Pour the filling into the crust and bake for 10 minutes. Lower the oven temperature to 350° and bake for about 25 minutes longer, until the filling is fully set. Transfer the pan to a rack and let cool completely. Cut into bars and serve with crème fraîche.
The pumpkin pie bars can be refrigerated for up to 2 days. Serve chilled or at room temperature.