Preheat oven to 350°F (175°C). Grease a 9x13-inch metal baking dish.
In a large bowl, whisk pumpkin, evaporated milk, eggs, sugar, cinnamon, ginger, nutmeg, and salt until smooth. Pour mixture into prepared pan.
Sprinkle cake mix evenly over pumpkin layer. Do not stir.
Drizzle melted butter across the dry cake mix. Use a spoon to lightly spread it over dry patches, but don't mix it in. A few dry patches are ok - the moisture from the cake bubbles up.
Bake 45–55 minutes, until top is golden brown and set around the edges but still have some jiggle in the middle. For foolproof doneness testing, the internal temp at the center should reach 175°F (79°C).
Cool at least 1 hour before serving. The pumpkin layer will firm up significantly as it cools.
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Notes
The internal temp at the center should reach about 175°F–180°F (79°C–82°C). At this range, the eggs are fully set but the filling is still creamy. If it’s under 170°F, it will be too loose and won’t hold once cooled.Edges set first: The custard bakes from the outside in, so the edges firm up while the center stays softer.Cooling is key: Like pumpkin pie, the filling needs 30–60 minutes minimum to cool so it can finish setting. Straight out of the oven, it will be jiggly and too soft. Serve warm, if you like, but still wait at least 30 minutes.Use a metal pan: It promotes crisp edges and deeper browning.You can swap yellow cake mix for spice cake mix.Storage: Stays good in the fridge up to 4 days.