Preheat oven to 350°F. Line four 7 inch pans or three 8 inch round pans with parchment rounds, and grease with non-stick cooking spray.

Mix together all dry ingredients (flour, baking powder, sugar, cinnamon, ginger, nutmeg, and salt) in a stand mixer with a paddle attachment until fully combined.

Mix chunks of room-temperature butter slowly into the dry mix, on a low speed. Continue to mix until no large chunks of butter remain, and the mixture becomes crumbly.

Pour in egg whites, and mix on low until just incorporated.

Mix in the sour cream, then the pumpkin puree on a low speed.

Add in vanilla and oil, and mix at a low speed until fully incorporated. Scrape down the sides of the bowl with a spatula, then beat on low speed for about 15 seconds.

Divide batter evenly between the prepared cake pans.

Bake for 33 minutes, or until a toothpick comes out clean. Allow the pans to cool for 10 minutes, then run an offset spatula around perimeter of the pan to separate the cake from the pan.

Place cake layers into the freezer for 45 minutes, to accelerate the cooling process. Once the layers are fully cooled, carefully flip the pans and remove the layers from the pans.

Use a serrated knife to level the tops of the layers, and save in a bowl to make the pumpkin stump.

While the cake layers bake and cool, make the cream cheese buttercream frosting.

Beat the butter and cream cheese on a medium speed for 30 seconds with a paddle attachment, until smooth. Slowly add in the powdered sugar, 1 cup at a time. Alternate with small splashes of cream.

Once fully mixed, add in the vanilla and salt, and beat on low until the ingredients are fully incorporated, and the desired consistency is reached. 

If the frosting is too thick, add in additional cream (1 TBSP at a time). If the frosting is too thin, add in more powdered sugar (quarter of a cup at a time).

Stack and frost the pumpkin cake layers on a greaseproof cake board, using a dab of frosting to help stick the first cake layer to the board.

Add an even layer of buttercream between each cake layer.

Apply a thin coat of frosting around the cake, to fully cover the cake layers. Smooth using a bench scraper, then chill the cake in the fridge (20 minutes) or freezer (5 minutes) until the frosting is firm to the touch.

Add a second, thicker layer of frosting to the cake, and smooth using a bench scraper.

Chill in the fridge for at least an hour, then paint pumpkins around the cake using a mixture of gel food coloring and vodka (1 tsp of vodka mixed with 1-2 dros of gel food coloring).

Paint multiple layers of the food coloring mixture to create dimension and depth, chilling the cake as need if the frosting begins to soften.