Preheat the oven to 350°F (175°C) and grease a 9x13-inch baking pan.
In a large bowl, whisk together the pumpkin puree, sweetened condensed milk, sour cream, melted butter, egg, granulated sugar, pumpkin pie spice, and salt until smooth.
Pour the mixture into the prepared baking pan and spread evenly.
Evenly sprinkle the dry yellow cake mix over the top of the pumpkin mixture. Do not stir.
Sprinkle chopped walnuts or pecans and raisins (if using) over the top.
Bake for 45-50 minutes, or until the top is golden brown and bubbling at the edges.
Remove from the oven and let cool for 10 minutes before serving.
Serve warm with whipped cream or vanilla ice cream for an extra treat!
Notes
For best results, ensure the cake mix is evenly distributed for a consistent crispy topping.