Preheat the oven to 350°F and line a baking sheet with parchment paper.

In a large mixing bowl, combine the spice cake mix, eggs, pumpkin puree, and optional 1/2 teaspoon vanilla extract, then mix with a fork, hand mixer, or stand mixer until combined; the dough will be wet and sticky like a thick batter, so do not add flour, oil, or water from the cake mix box directions.

Scoop heaping tablespoonfuls of dough onto the parchment-lined baking sheet, leaving about 2 inches between them, and gently pat the tops down slightly.

Bake for 9 to 10 minutes, until the edges look lightly golden and the centers are set.

Let the cookies cool on the baking sheet for about 5 minutes, then transfer them to a wire rack to cool completely before frosting.

While the cookies cool, beat the softened cream cheese and softened butter together on low speed in a medium bowl until smooth and free of lumps.

Add the powdered sugar, 1 teaspoon pure vanilla extract, and 1/4 teaspoon of the cinnamon, then beat until smooth and spreadable.

Spoon or spread the frosting over the cooled cookies, sprinkle with the remaining 1/4 teaspoon cinnamon if desired, and serve right away.