Preheat your oven to 325 degrees. Spray four 6-inch pans or three 8-inch pans with cooking spray, line with parchment paper, and spray again. Set aside.
In a medium sized bowl, combined the flour, baking powder, cardamon, ground cinnamon, ginger, nutmeg, and salt. Set aside.
In a stand sized mixer fitted with the paddle attachment, cream the sugar and eggs on medium speed until they are light and fluffy, about 4 minutes.
Add the oil and vanilla and beat on medium until fully incorporated, about 30 seconds. Add the pumpkin puree and mix until combined, about 30 seconds.
With the mixer on the lowest speed, gradually add the dry ingredients to the pumpkin/egg mixture.
Evenly distribute the pumpkin batter to the prepped cake pans. With the back of a spoon, even out the batter to ensure it’s smooth for baking.
Before putting the cake into the oven, make the cinnamon swirl. Mix the brown sugar, flour, and cinnamon together until combined. Add in the melted butter and mix just until combined. Add immediately to the cake batter because the longer it sits out, the harder it will get as the butter solidifies.
Drop small spoonfuls of the cinnamon mixture on each of the cake layers. Use a knife or toothpick to gently swirl the spoonfuls into the batter. It’s normal to have some pieces remain as chunks and some that swirl into the batter.
Bake for 30-35 minutes. Check the cake by inserting a toothpick. It’s done when it comes out with just a few moist crumbs on it.
Cool 10-20 minutes before transferring the cakes out of the pans and onto a cooling rack. Cool completely before wrapping with plastic wrap and then refrigerate, if you’re not going to be using them until the next day.
For the buttercream
In the bowl of a stand mixer fitted with the paddle attachment, beat the butter on medium-high speed until creamy, about 3 minutes. With a rubber spatula, scrape down the sides of the bowl.
Once the butter is creamed, add the brown sugar and beat on medium-high speed until combined, about 1 minute.
Add the cinnamon, powdered sugar, heavy cream, vanilla extract, and salt. Turn the mixer on low and mix just until combined, about 30 seconds. Turn the mixer up to medium-high and beat until completely combined and creamy. If you crave extra flavor, add a little more cinnamon and/or vanilla extract.
With a rubber spatula, beat out the air pockets by hand until smooth and creamy
For the drip
Heat the cream in a microwave safe bowl for 60 seconds. Pour the cream over the white chocolate chips and cover with plastic wrap. Let sit for five minutes. Stir until smooth.
Once cooled slightly, apply the ganache on a chill/cooled cake.
Assembly
Level cakes, if needed, and on a cake board, place a small dollop of frosting in the middle. This will act as “glue” for the cake.
Place one of the pumpkin cake layers top side up on the cake board. Apply about 1 cup of the buttercream and with an offset spatula, evenly distribute it around the cake. Drizzle some of the white chocolate ganache on top of the snickerdoodle buttercream. Repeat this step.
Place the last pumpkin cake layer, top side down onto the white ganache and buttercream, and apply another cup of frosting.
Apple a thin coat of the buttercream around the cake and freeze for 10-15 minutes. This is your crumb coat, which helps secure the crumbs onto the cake.
Apply the rest of the frosting to the cake and then add your drip. Serve at room temperature.