Preheat oven to 350 degrees.
In a bowl, whisk together the pumpkin, evaporated milk, sugar, pumpkin pie spice, and eggs.
Pour into a greased 9x13 (or similar) baking dish. Sprinkle entire cake mix on top. Sprinkle pecans over cake mix. Place pats of butter over the top, covering as evenly and as much of the cake as you can.
Bake at 350 for about 40 minutes. A toothpick or knife inserted into the center should come out mostly clean when it’s ready (a little pumpkin on the knife is ok).
Let cool before serving. Tastes best room temp but you can store leftovers in the refrigerator for several days.