Preheat the oven to 350 degrees and line a 6-inch round cake pan with parchment.
In a bowl, stir together the flour, 1/2 cup granulated sugar, pumpkin pie spice, and baking soda. Add the pumpkin puree, egg, and oil, then mix until smooth.
In a separate bowl, beat the cream cheese with 2 tablespoons granulated sugar, the egg yolk, and vanilla until creamy.
Pour half the pumpkin batter into the pan. Spoon the cream cheese mixture over it, then top with the remaining pumpkin batter. Smooth the surface.
Bake for 35 minutes, or until a toothpick inserted in the center comes out clean. Cool the cake completely in the pan.
Beat the butter with the powdered sugar until fluffy. Add orange food coloring a drop at a time until the frosting reaches a bright shade. Spread the frosting over the cooled cake.
Use the black decorating gel to draw eyes, a nose, and a mouth on the frosting to create the jack-o’-lantern face.