Preheat oven to 350 degrees.
Heat butter until just melted, not hot. Whisk in one egg. Mix in yellow cake mix with a fork until mixture resembles crumbs.
Sprinkle 1/2 of the crumbs into a greased 9x13 pan, setting aside the remainder.
Beat 4 remaining eggs in a large bowl and the stir in pumpkin.
In a small bowl, mix sugar and spices, then mix into the pumpkin/eggs.
Stir in evaporated milk 1/2 can at a time.
Pour pumpkin mix over crust, then sprinkle remaining crumbs on top - pan will be quite full.
Bake for 60-70 minutes (a knife inserted near the edge will come out clean, but the center may still be soft).
Cool completely and chill before serving with whipped cream or cool whip.