Preheat oven to 350°F degrees.
Grease a 9-inch round cake pan with cooking spray.
In a medium bowl, whisk together the flour and baking soda. Set aside.
In a large bowl, beat the butter, brown sugar, and white sugar with an electric hand mixer until creamy and smooth, about 1 minute. Add the instant pudding mix and beat until combined.
Add the eggs and vanilla, and beat until combined. Finally, add the flour mixture and beat until combined and a uniform batter forms. Stir or beat in the chocolate chips.
Pour the batter into the greased cake pan and spread evenly around pan.
Bake for 30-35 minutes, or until the edges are golden brown and the middle is firm. A toothpick should come out clean or with a few crumbs, but no batter. You may need to loosely cover the cake with foil for the last 15 minutes if the edges are getting too dark.
While the cookie cake is still warm from the oven, arrange the gelt on top. Let cool completely on a wire rack before frosting.
To frost, fit a disposable frosting bag with a frosting tip (I used the Milton 1M tip). Fill your bag with store-bought frosting or your favorite homemade frosting and pipe onto the cookie cake. Add sprinkles. Enjoy!