Preheat your oven to 350°F (175°C) and grease a 9x13 inch baking pan.

In a large bowl, whisk together the pure pumpkin, evaporated milk, light brown sugar, eggs, and pumpkin pie spice until smooth.

Pour the pumpkin mixture into the prepared baking pan, spreading it evenly.

Evenly sprinkle the yellow cake mix over the pumpkin layer without mixing.

Optionally add crushed graham crackers or chopped pecans on top.

Melt the unsalted butter and drizzle it over the cake mix.

Bake for 45-50 minutes, checking for doneness at the 45-minute mark.

Let cool for a few minutes before serving warm with vanilla ice cream or whipped cream.