Preheat the oven to 400°F (200°C). Lightly coat a 9-inch deep-dish pie dish with cooking spray.

Pulse the gingersnaps in a food processor until they form fine, even crumbs (about 1 cup). Transfer to a bowl and stir in the melted butter until the crumbs look like damp sand. Press the mixture firmly and evenly over the bottom of the pie dish; the flat bottom of a measuring cup works well.

In a large bowl, whisk or beat the pumpkin puree, evaporated milk, egg whites, salt, pumpkin pie spice, vanilla, and sugar until completely smooth. Gently pour the filling over the crust.

Bake at 400°F for 15 minutes, then reduce the oven temperature to 325°F (165°C) and bake for 40 to 45 minutes more, until the edges are set and a knife inserted near the center comes out clean. The very center can still have a slight wobble.

Cool the pie on a wire rack for at least 1 hour, then refrigerate for at least 2 hours, until fully set, before slicing.