How to Make It
Preheat oven to 350°F. Whisk together pumpkin, evaporated milk, sugar, eggs, and 1 teaspoon of the cinnamon in a medium bowl to combine. Pour mixture into a lightly greased 13- x 9-inch baking dish lined with parchment paper.
Sprinkle 1 1/2 cups of the cake mix evenly over top of pumpkin mixture; sprinkle with chopped pecans. Sprinkle remaining cake mix over nuts. (Do not stir!)
Drizzle butter evenly over cake mix. Bake in preheated oven until golden brown and set, about 50 minutes.
Cool to room temperature on a wire rack, about 1 hour. Invert pan onto a cutting board, and refrigerate at least 1 hour until well chilled. Trim edges, and cut into 24 squares.
Stir remaining 1/4 teaspoon cinnamon into whipped cream. Add mixture to a large ziplock plastic bag, and snip a small corner of the bag. Pipe whipped cream on top of each square. Garnish with 1 pecan half piece.