Preheat the oven to 350°F and generously spray three 8- or 9-inch round cake pans (or you can use one at a time) with cooking spray. Using a stand mixer fitted with the paddle attachment (or a large mixing bowl with a hand mixer), combine the butter, oil, sugars, eggs and vanilla extract and beat on medium speed until creamy and free of lumps. Add the pumpkin and mix until just combined.
In a separate bowl, combine the flour, baking powder, baking soda, salt and pumpkin pie spice. Mix well. Gradually add to the butter mixture and beat on medium speed until just combined. Divide the mixture evenly between the prepared cake pans and bake one at a time in the preheated oven for 25-30 minutes, or until a toothpick inserted into the centers come out clean. Let cool in pan for 5 minutes, remove from pan and let cool completely on a wire rack. Using a serrated bread knife, cut the rounded tops off each cooled cake.
PREPARE THE FROSTING
Using a stand mixer fitted with the whisk attachment (or a large mixing bowl with a hand mixer), mix the butter, cream cheese and vanilla until smooth. Add the confectioners’ sugar and beat on medium-high speed for 3 minutes.
Divide the frosting between three same-size bowls, adding a bit more to one than the other two. Keep the bowl with the most frosting white, not adding any food coloring. To one of the remaining bowls, add orange (or neon orange) food coloring and stir until deep orange in color. Add half the amount of food coloring to the last bowl and stir until light orange.
ASSEMBLE THE CAKE
Place one cake in the center of a rotating cake stand. Spread white frosting evenly and generously over the top in an even layer. Top with another cake and repeat with a layer of frosting. Top with the remaining cake.
Using the back of a spoon or an offset spatula, apply a row of the dark orange frosting to the outside of the bottom cake layer. Apply the light orange to the outside of the middle cake layer and apply the white to the outside of the top cake layer. Use the spatula (or spoon) to blend the frosting colors together as you rotate the cake stand. Drop the different frosting colors on the top and blend together, rotating the stand and using the offset spatula. Top with pumpkin candies, cover and refrigerate until ready to serve.
A cream cheese based buttercream needs to be stored in the refrigerator and is good for about a week. When getting ready to use it again, give it a few minutes to come to room temperature.
If you don’t think you’ll have a use for it right away, freeze it! That’ll give you a couple of months to put it away and then make another batch of these cookies.