In a large mixing bowl, combine the cake mix and pumpkin puree. Using a hand mixer or stand mixer, beat until the mixture is smooth and evenly blended.
Lightly spray a 9×9-inch baking pan with nonstick spray. Spread the batter evenly into the pan. The mixture will be thick, so use a spatula to smooth it out.
In a medium bowl, beat together the softened cream cheese, sugar, vanilla, and egg yolk until smooth and creamy.
Drop large spoonfuls of the cream cheese mixture over the pumpkin batter. Use a knife to gently swirl the two layers together, being careful not to overmix so the swirl pattern remains visible.
Bake for 35–45 minutes, or until a toothpick inserted in the center comes out clean. Allow to cool slightly before serving. Enjoy!