In a large mixing bowl, combine the pumpkin purée, evaporated milk, eggs, sugar, cinnamon, salt, and pumpkin pie spice. Whisk until smooth and well blended.
Grease a 9x13-inch baking dish. Pour the pumpkin mixture into the prepared baking dish and spread it evenly.
Evenly sprinkle the dry yellow cake mix over the pumpkin mixture.
Evenly drizzle the melted butter over the cake mix, aiming to cover as much of the surface as you can.
Bake for 45 minutes, or until the top is golden brown and the edges are set.
Let the cake cool for at least 15 minutes before serving. Enjoy it warm or at room temperature with whipped cream or ice cream.